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ILLUSIONS 
A 
PSYCHOLOGICAL,STUDY 
BY 
JAMES SULLY 
PART I 
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THE HUMBOLDT PUBLISHING CO. ILLUSIONS: 
A PSYCHOLOGICAL STUDY. 
By JAMES SULLY, 
Author of “ Sensation and Intuition,” “ Pessimism,” etc. 
IN TWO PARTS.—PART FIRST. 
PREFACE. 
creatures, hardly distinguishable from the 
admittedly insane. And this way of thinking 
of illusion and its subjects is strengthened 
by one of the characteristic sentiments of 
our age. The nineteenth century intelligence 
plumes itself on having got at the bottom oi 
mediaeval visions and church miracles, and 
it is wont to commiserate the feeble minds 
that are still subject to these self-deceptions. 
According to this view, illusion is some- 
thing essentially abnormal and allied to in- 
sanity. And it would seem to follow that 
its nature and origin can be best studied by 
those whose speciality it is to observe the 
phenomena of abnormal life. Scientific pro- 
cedure has in the main conformed to this 
distinction of common sense. The phenom- 
ena of illusion nave ordinarily been investi- 
gated by alienists, that is to say, physicians 
who are brought face to face with their most 
striking forms in the mentally deranged. 
While there are very good reasons for 
this treatment of illusion as a branch of 
mental pathology, it is by no means certain 
it can be a complete and exhaustive one. 
Notwithstanding the flattering supposition 
of common sense, that illusion is essentially 
an incident in abnormal life, the careful 
observer knows well enough that the case 
is far otherwise. 
There is, indeed, a view of our race dia- 
metrically opposed to the flattering opinion 
referred to above, namely, the humiliating 
judgment that all men habitually err, or that 
illusion is to be regarded as the natural con- 
dition of mortals. This idea has found ex- 
pression, not only in the cynical exclamation 
of the misanthropist that most men are fools, 
but also in the cry of despair that sometimes 
The present volume takes a wide survey 
of the field of error, embracing in its view 
not only the illusions of sense dealt with in 
treatises on physiological optics, etc., but 
also other errors familiarly known as illu- 
sions, and resembling the former in their 
structure and mode of origin. I have through- 
out endeavored to keep to a strictly scientific 
treatment, that is to say, the description and 
classification of acknowledged errors, and 
the explanation of these by a reference to 
their psychical and physical conditions. At 
the same time, I was not able, at the close of 
my exposition, to avoid pointing out how the 
psychology leads on to the philosophy of the 
subject. Some of the chapters were first 
roughly sketched out in articles published in 
magazines and reviews ; but these have been 
not only greatly enlarged, but, to a consider- 
able extent, rewritten. 
J.S. 
Hampstead, April, 18S1. 
CHAPTER I. 
THE STUDY OF ILLUSION. 
Common sense, knowing nothing of fine 
distinctions, is wont to draw a sharp line 
between the region of illusion and that of 
sane intelligence. To be the victim of an 
illusion is, in the popular judgment, to be 
excluded from the category of rational men. 
The term at once calls up images of stunted 
figures with ill-developed brains, half-witted 2 
ILLUSIONS: 
breaks from the weary searcher after absolute 
truth, and from the poet when impressed 
with the unreality of his early ideals. 
Without adopting this very disparaging 
opinion of the intellectual condition of man- 
kind, we must recognize the fact that most 
men are sometimes liable to illusion. Hard- 
ly anybody is always consistently sober and 
rational in his perceptions and beliefs. A 
momentary fatigue of the nerves, a little 
mental excitement, a relaxation of the effort 
of attention by which we continually take 
our bearings with respect to the real world 
about us, will produce just the same kind of 
confusion of reality and phantasm which we 
observe in the insane. To give but an ex- 
ample : the play of fancy which leads to a 
detection of animal and other forms in clouds, 
is known to be an occupation of the insane, 
and is rightly made use of by Shakespeare 
as a mark of incipient mental aberration in 
Hamlet; and yet this very same occupation 
is quite natural to children, and to imagina- 
tive adults when they choose to throw the 
reins on the neck of their phantasy. Our 
luminous circle of rational perception is 
surrounded by a misty penumbra of illusion. 
Common sense itself may be said to admit 
this, since the greatest stickler for the en- 
lightenment of our age will be found in 
practice to accuse most of his acquaintance 
at some time or another of falling into 
illusion. 
If illusion thus has its roots in ordinary 
mental life, the study of it would seem to 
belong to the physiology as much as to the 
pathology of mind. We may even go fur- 
ther, and say that in the analysis and expla- 
nation of illusion the psychologist may be 
expected to do more than the physician. If, 
on the one hand, the latter has the great 
privilege of observing the phenomena in their 
highest intensity, on the other hand, the 
former has the advantage of being familiar 
with the normal intellectual process which 
all illusion simulates or caricatures. To this 
it must be added that the physician is natu- 
rally disposed to look at illusion mainly, if 
not exclusively, on its practical side, that is, 
as a concomitant and symptom of cerebral 
disease, which it is needful to be able to rec- 
ognize. The psychologist has a different 
interest in the subject, being especially con- 
cerned to understand the mental antecedents 
of illusion and its relation to accurate per- 
ception and belief. It is pretty evident, in- 
deed, that the phenomena of illusion form a 
region common to the psychologist and the 
mental pathologist, and that the complete 
elucidation of the subject will need the co- 
operation of the two classes of investigator. 
In the present volume an attempt will be 
made to work out the psychological side of 
the subject; that is to say, illusions will be 
viewed in their relation to the process of just 
and accurate perception. In the carrying 
out of this plan our principal attention will 
be given to the manifestations of the illusory 
impulse in normal life. At the same time, 
though no special acquaintance with the 
pathology o£ the subject will be laid claim 
to, frequent references will be made to the 
illusions of the insane. Indeed, it will be 
found that the two groups of phenomena— 
the illusions of the normal and of the abnor- 
mal condition—are so similar, and pass into 
one another by such insensible gradations, that 
it is impossible to discuss the one apart from 
the other. The view of illusion which will 
be adopted in this work is that it constitutes 
a kind of borderland between perfectly sane 
and vigorous mental life and dementia." 
And here at once there forces itself on our 
attention the question, What exactly is to be 
understood by the term “ illusion ” ? In 
scientific works treating of the pathology of 
the subject, the word is confined to what are 
specially known as illusions of the senses, 
that is to say, to false or illusory perceptions. 
And there is very good reason for this limi- 
tation, since such illusions of the senses are 
the most palpable and striking symptoms 
of mental disease. In addition to this, it 
must be allowed that, to the ordinary reader, 
the term first of all calls up this same idea 
of a deception of the senses. 
At the same time, popular usage has long 
since extended the term so as to include un- 
der it errors which do not counterfeit actual 
perceptions. We commonly speak of a man 
being under an illusion respecting himself 
when he has a ridiculously exaggerated view 
of his own importance, and in a similar way 
of a person being in a state of illusion with 
respect to the past when, through frailty of 
memory, he pictures it quite otherwise than 
it is certainly known to have been. 
It will be found, I think, that there is a 
very good reason for this popular extension 
of the term. The errors just alluded to have 
this in common with illusions of sense, that 
they simulate the form of immediate or self- 
evident cognition. An idea held respecting 
ourselves or respecting our past history does 
not depend on any other piece of knowledge ; 
in other words, is not adopted as the result 
of a process of reasoning. What I believe 
with reference to my past history, so far as I 
can myself recall it, I believe instantaneously 
and immediately, without the intervention of 
any premise or reason. Similarly, our no- 
tions of ourselves are, for the most part, ob- 
tained apart from any process of inference. 
The view which a man takes of his own char- 
acter or claims on society he is popularly 
supposed to receive intuitively by a mere act 
of internal observation. Such beliefs may 
not, indeed, have all the overpowering force 
which belongs to illusory perceptions, for the 
intuition of something by the senses is com- 
monly looked on as the most immediate and 
irresistible kind of knowledge. Still, they 
must be said to come very near illusions of 
sense in the degree of their self-evident cer- 
tainty. 
Taking this view of illusion, we may pro- 
visionally define it as any species of error 
which counterfeits the form of immediate. A PSYCHOLOGICAL STUDY 
or intuitive knowledge, whether 
as sense-perception or otherwise. Whenever 
a thing is believed on its own evidence and 
not as a conclusion from something else, and 
the thing then believed is demonstrably wrong, 
there is an illusion. The term would thus 
appear to cover all varieties of error which 
are not recognized as fallacies or false infer- 
ences. If for the present we roughly divide 
all our knowledge into the two regions of 
primary or intuitive, and secondary or infer- 
ential knowledge, we see that illusion is false 
-or spurious knowledge of the first kind, fal- 
lacy false or spurious knowledge of the sec- 
ond kind. At the same time, it is to be re- 
membered that this division is only a very 
rough one. As will appear in the course of 
our investigation, the same error may be 
called either a fallacy or an illusion, accord- 
ing as we are thinking of its original mode of 
production or of the form which it finally as- 
sumes ; and a thorough-going psychological 
analysis of error may discover that these two 
classes are at bottom very similar. 
As we proceed, we shall, I think, find an 
ample justification for our definition. We 
shall see that such illusions as those respect- 
ing ourselves or the past arise by very much 
the same mental processes as those which are 
■discoverable in the production of illusory 
perceptions; and thus a complete psychology 
of the one class will, at the same time, contain 
the explanation of the other classes. 
The reader is doubtless aware that philos- 
ophers have still further extended the idea 
of illusion by seeking to bring under it beliefs 
which the common sense of mankind has al- 
ways adopted and never begun to suspect. 
Thus, according to the idealist, the popular 
notion (the existence of which Berkeley, how- 
ever, denied) of an external world, existing 
in itself and in no wise dependent on our 
perceptions of it, resolves itself into a grand 
illusion of sense. 
At the close of our study of illusions we 
shall return to this point. We shall there 
inquire into the connection between those 
illusions which are popularly recognized as 
such, and those which first come into view 
or appear to do so (for we must not vet as- 
sume that there are such) after a certain kind 
of philosophic reflection. And some attempt 
will be made to determine roughly how far 
the process of dissolving these substantial 
beliefs of mankind into airy phantasms may 
venture to go. 
For the present, however, these so-called 
illusions in philosophy will be ignored. It 
is plain that illusion exists only in antithesis 
to real knowledge. This last must be as- 
sumed as something above all question. 
And a rough and provisional, though for our 
purpose sufficiently accurate, demarkation of 
the regions of the real and illusory seems to 
coincide with the line which common sense 
draws between what all normal men agree in 
holding and what the individual- holds, 
whether temporarily or permanently, in con- 
tradiction to this. For our present purpose 
! the real is that which is true for all. Thus, 
I though physical science may tell us that there 
is nothing corresponding to our sensations of 
color in the world of matter and motion 
which it conceives as surrounding us; yet, 
inasmuch as to all men endowed with the 
normal color-sense the same material objects 
appear to have the same color, we may speak 
of any such perception as practically true, 
marking it off from those plainly illusory 
perceptions which are due»to some subjective 
cause, as, for example, fatigue of the retina. 
To sum up: in treating of illusions we 
shall assume, what science as distinguished 
from philosophy is bound to assume, namely, 
that human experience is consistent; that 
men’s perceptions and beliefs fall into a con- 
sensus. From this point of view illusion is 
seen to arise through some exceptional feat- 
ure in the situation or condition of the indi- 
vidual, which, for the-time, breaks the chain 
of intellectual solidarity which under ordinary 
circumstances binds the single member to 
the collective body. Whether the common 
experience which men thus obtain is rightly 
interpreted is a question which does not con- 
cern us here. For our present purpose, 
which is the determination and explanation 
of illusion as popularly understood, it is suffi- 
cient that there is this general consensus of 
belief, and this may provisionally be regarded 
as at least practically true. 
CHAPTER II. 
THE CLASSIFICATION OF ILLUSIONS. 
If illusion is the simulation of immediate 
knowledge, the most obvious mode of class- 
ifying illusions would appear to be accord- 
ing to the variety of the knowledge which 
they simulate. 
Now, the popular psychology that floats 
about in the ordinary forms of language has 
long since distinguished certain kinds of un- 
reasoned or uninferred knowledge. Of these 
the two best known are perception and mem- 
ory. When I see an object before me, or 
when I recall an event in my past experience, 
l am supposed to grasp a piece of knowledge 
directly, to know something immediately, 
and not through the medium of something 
else. Yet I know differently in the two 
cases. In the first I know by what is called 
a presentative process, namely, that of sense- 
perception ; in the second I know by a rep- 
resentative process, namely, that of repro- 
duction, or on the evidence of memory. In 
the one case the object of cognition is pres- 
ent to my perceptive faculties; in the other 
it is recalled by the power of memory. 
Scientific psychology tends, no doubt, to 
break down some of these popular distinc- 
tions. Just as the zoologist sometimes groups 
together varieties of animals which the un- 
scientific eye would never think of connect- 
ing, so the psychologist mav analyze mental 4 
ILLUSIONS: 
operations which appear widely dissimilar to 
the popular mind, and reduce them to one 
fundamental process. Thus recent psychol- 
ogy draws no sharp distinction between per- 
ception and recollection. It finds in both 
very much the same elements, though com- 
bined in a different way. Strictly speaking, 
indeed, perception must be defined as a pre- 
sentative-representative operation. To the 
f sychologist it comes to very much the same 
thing whether, fqr example, on a visit to 
Switzerland, our minds are occupied in per- 
ceiving the distance of a mountain or in re- 
membering some pleasant excursion which 
we made to it on a former visit. In both 
cases there is a reinstatement of the past, a 
reproduction of earlier experience, a process 
of adding to a present impression a product 
of imagination—taking this word in its widest 
sense. In both cases the same laws of repro- 
duction or association are illustrated. 
Just as a deep and exhaustive analysis of 
the intellectual operations thus tends to 
identify their various forms as they are dis- 
tinguished by the popular mind, so a thor- 
ough investigation of the flaws in these 
operations, that is to say, the counterfeits of 
knowledge, will probably lead to an identifi- 
cation of the essential mental process which 
underlies them. It is apparent, for example, 
that, whether a man projects some figment 
of his imagination into the external world, 
giving it present material reality, or whether 
(if I may be allowed the term) he retrojects it 
into the dim region of the past, and takes it 
for a reality that has been, he is committing 
substantially the same blunder. The source 
of the illusion in both cases is one and the 
same. 
It might seem to follow from this that a 
scientific discussion of the subject would 
overlook the obvious distinction between 
illusions of perception and those of memory; 
that it would attend simply to differences in 
the mode of origination of the illusion, what- 
ever its external form. Our next step, then, 
would appear to be to determine these dif- 
ferences in the mode of production. 
That there are differences in the origin 
and source of illusion is a fact which has 
been fully recognized by those writers who 
have made a special study of sense-illusions. 
By these the term illusion is commonly em- 
ployed in a narrow, technical sense, and 
opposed to hallucination. An illusion, it is 
said, must always have its starting-point in 
some actual impression, whereas a hallucina- 
tion has no such basis. Thus it is an illusion 
when a man, under the action of terror, takes 
a stump of a tree, whitened by the moon’s 
rays, for a ghost. It is a hallucination when 
an imaginative person so vividly pictures to 
himself the form of some absent friend that, 
for the moment, he fancies himself actually 
beholding him. Illusion is thus a partial 
displacement of external fact by a fiction of 
the imagination, while hallucination is a 
total displacement. 
This distinction, which has been adopted 
by the majority of recent alienists,* is aval* 
uable one, and must not be lost sight of here. 
It would seem, from a psychological point of. 
view, to be an important circumstance in the 
genesis of a false perception whether the 
intellectual process sets out from within or 
from without. And it will be found, more- 
over, that this distinction may be applied to' 
all the varieties of error which I propose to 
consider. Thus,-for example, it will be seen 
further on that a false recollection may set 
out either from the idea of some actual past 
occurrence or from a present product of the 
imagination. 
It is to be observed, however, that the line 
of separation between illusion and halluci- 
nation, as thus defined, is a very narrow one. 
In by far the largest number of hallucina- 
tions it is impossible to prove that there is 
no modicum of external agency co-operating 
in the production of the effect. It is pre- 
sumable, indeed,- that many, if not all, hallu- 
cinations have such a basis of fact. Thus,, 
the madman who projects his internal 
thoughts outward in the shape of external 
voices may, for aught we know, be prompted 
to do so in part by faint impressions coming 
from the ear,- the result of those slight stim- 
ulations to which the organ is always ex- 
posed, even in profound silence, and which 
in his case assume an exaggerated intensity. 
And ever if it is clearly made out that there 
are hallucinations in the strict sense, that is 
to say, false perceptions which are wholly 
due to internal causes, it must be conceded 
that illusion shades off into hallucination by 
steps which it is impossible for science tx> 
mark. In many cases it must be left an open 
question whether the error is to be classed 
as an illusion or as a hallucination.t 
For these reasons, I think it best not to 
make the distinction between illusion and 
hallucination the leading principle of my 
classification. However important psycho- 
logically, it does not lend itself to this pur- 
pose. The distinction must be kept in view 
and illustrated as far as possible. Accord- 
ingly, while in general following popular 
usage and employing the term illusion as the 
generic name, I shall, when convenient, recog- 
nize the narrow and technical sense of the 
term as answering to a species co-ordinate 
with hallucination. 
Departing, then, from what might seem 
the ideally best order of exposition, I propose 
after all to set out with the simple popular 
scheme of faculties already referred to. Even 
* A history of the distinction is given by Brierre 
de Boismont, in his work On Illusions (translated 
by K. T. Hulme, 1859). He says that Arnold (1806) 
first defined hallucination, and distinguished it from 
illusion. Esquirer, in his work, Des Maladies 
Montales (1838), may be said to have fixed the dis- 
tinction. (See Hunt’s translation, 1845, p. in.) 
t This fact has been fully recognized by writers 
on the pathology of the subject; for example, 
Griesinger, Mental Pathology and Therapeutics 
(London, 1867), p. 84; Baillarger, article, “Des 
Hallucinations,” in the M4moires de TAcadeun'e 
Royale de Mifdecine, tom. xii. p. 273, etc.; Wundt 
Physiologische Psychologies p. 653. A PSYCHOLOGICAL STUDY. 
if they are, psychologically considered, ident- 
ical operations, perception and memory are 
in general sufficiently marked off by a special- 
ity in the form of the operation. Thus, while 
memory is the of something 
with a special reference of consciousness to 
its past existence, perception is the reproduc- 
■tion of something with a special reference to 
its present existence as a part of the presented 
object. In other words, though largely rep- 
resentative when viewed as to its origin, per- 
•ception is presentative in relation to the object 
•which is supposed to be immediately present 
to the mind at the moment.* Hence the con- 
venience of recognizing the popular classifi- 
cation, and of making it our starting-point in 
the present case. 
All knowledge which has any appearance 
of being directly reached, immediate, or self- 
evident, that is to say, of not being inferred 
from other knowledge, may be divided into 
four principal varieties: Internal Perception 
or Introspection of the mind’s own feelings; 
External Perception; Memory; and Belief, 
in so far as it simulates the form of direct 
knowledge. The first is illustrated in a man’s 
consciousness of a present feeling of pain or 
pleasure. The second and the third kinds 
•have already been spoken of, and are too 
• familiar to require illustration. It is only 
■needful to remark here that, under perception, 
or rather in close conjunction with it, I pur- 
pose dealing with the knowledge of others’ 
feelings, in so far as this assumes the aspect 
of immediate knowledge. The term belief 
is here used to include expectations and any 
other kinds of conviction that do not fall 
•under one of the other heads. An instance 
of a seemingly immediate belief would be a 
prophetic prevision of a coming disaster, or 
a man’s unreasoned persuasion as to his own 
powers of performing a difficult task. 
It is, indeed, said by many thinkers that 
there are no legitimate immediate beliefs; 
that all our expectations and other convictions 
about things, in so far as they are sound, must 
repose on other genuinely immediate knowl- 
edge, more particularly sense-perception and 
memory. This difficult question need not be 
discussed here. It is allowed by all that there 
is a multitude of beliefs which we hold tena- 
ciously and on which we are ready to act, 
which, to the'mature mind, wear the appear- 
ance of intuitive truths, owing their cogency 
to nothing beyond themselves. A man’s be- 
lief in his own merits, however it may have 
been first obtained, is as immediately assured 
to him as his recognition of a real object in 
the act of sense-perception. It may be added 
that many of our every-day working beliefs 
about the world in which we live, though 
presumably derived from memory and per- 
ception, tend to lose all traces of their origin 
and'to simulate the aspect of intuitions. Thus 
the proposition that logicians are in the habit 
! of pressing on our attention, that “ Men are 
mortal,” seems, on the face of it, to common 
sense to be something very like a self-evident 
truth, not depending on any particular facts 
of experience. 
In calling these four forms of cognition 
immediate, I must not, however, be supposed 
to be placing them on the same logical level. 
It is plain, indeed, to a reflective mind that, 
though each may be called immediate in this 
superficial sense, there are perceptible dif- 
ferences in the degree of their immediacy. 
Thus it is manifest, after a moment’s reflec- 
tion, that expectation, so far as it is just, is 
not primarily immediate in the sense in which 
purely presentative knowledge is so, since it 
can be shown to follow from something else. 
So a general proposition, though through 
familiarity and innumerable illustrations it 
has acquired a self-evident character, is seen 
with a very little inspection to be less funda- 
! mentally and essentially so than the proposi- 
tion, “ I am now feeling pain;” and it will 
be found that even with respect to memory, 
when the remembered event is at all remote, 
the process of cognition approximates to a 
mediate operation, namely, one of inference. 
What the relative values of these different 
kinds of immediate knowledge are is a point 
which will have to be touched on at the end 
of our study. Here it must suffice to warn 
the reader against the supposition that this 
value is assumed to be identical. 
It might seem at a first glance to follow 
from this four-fold scheme of immediate or 
quasi-immediate knowledge that there are 
four varieties of illusion. And this is true 
in the sense that these four heads cover all 
the main varieties of illusion. If there are 
only four varieties of knowledge which can 
lay any claim to be considered "immediate, it 
must be that every illusion will simulate the 
form of one of these varieties, and so be refer- 
able to the corresponding division. 
But though there are conceivably these 
four species of illusion, it does not follow 
that there are any actual instances of each 
class forthcoming. This we cannot determine 
till we have investigated the nature and ori- 
gin of illusory error. For example, it might 
be found that introspection, or the immediate 
inspection of our own, feelings or mental 
states, does not supply the conditions neces- 
sary to the production of such error. And 
indeed, it is probable that most persons, an- 
tecedently to inquiry, would be disposed to 
say that to fall into error in the observation 
of what is actually going on in our own 
minds is impossible. 
With the exception of this first division, 
however, this scheme may easily be seen to 
answer to actual phenomena. That there 
are illusions of perception is obvious, since it 
is to the errors of sense that the term illusion 
has most frequently been confined. It is 
hardly less evident that there are illusions of 
memory. The peculiar difficulty of distin- 
guishing between a past real event and a 
mere phantom of the imagination, illustrated 
* I here touch on the distinction between the 
psychological and the philosophical view of percep- 
tion, to be brought out more fully by and by. ILLUSIONS; 
in the exclamation, “ I either saw it or dreamt 
it,” sufficiently shows that memory is liable 
to be imposed on. Finally, it is agreed by 
all that the beliefs we are wont to regard as 
self-evident are sometimes erroneous. When, 
for example, an imaginative woman says she 
knows, by mere intuition, that something 
interesting is going to happen, say the arrival 
of a favorite friend, she is plainly running the 
risk of being self-deluded. So, too, a man’s 
estimate of himself, however valid for him, 
may turn out to be flagrantly false. 
In the following discussion of the subject 
I shall depart from the above order in so far 
as to set out with illusions of sense-percep- 
tion. These are well ascertained, forming, 
indeed, the best-marked variety. And the 
explanation of these has been carried much 
further than that of the others. Hence, 
according to the rule to proceed from the 
known to the unknown, there will be an ob- 
vious convenience in examining these first of 
all. After having done this, we shall be in a 
position to inquire whether there is anything 
analogous in the region of introspection or 
internal perception. Our study of the errors 
of sense-perception will, moreover, prove the 
best preparation for an inquiry into the nature 
and mode of production of the remaining 
two varieties. * 
I would add that, in close connection with 
the first division, illusions of perception, I 
shall treat the subtle and complicated phe- 
nomena of dreams. Although containing 
elements which ought, according to strictness, 
to be brought under one of the other heads, 
they are, as their common appellation, “vis- 
ions,”'shows, largely simulations of external 
and more especially visual, perception. 
Dreams are no doubt sharply marked off 
from illusions of sense-perception by a num- 
ber of special circumstances. Indeed, it 
may be thought that they cannot be ade- 
quately treated in a work that aims prima- 
rily at investigating the illusions of normal 
life, and should rather be left to those who 
make the pathological side of the subject 
their special study. Yet it may, perhaps, be 
said that in a wide sense dreams are a feat- 
ure of normal life. And, however this be, 
they have quite enough in common with 
other illusions of perception to justify us in 
dealing with them in close connection with 
these. 
is to say, those of sense. They are some- 
times called deceptions of the senses; but 
this is a somewhat loose expression, suggest- 
ing that we can be deceived as to sensation 
itself, though, as we shall see later on, this 
is only true in a very restricted meaning of 
the phrase. To speak correctly, sense-illu- 
sions must be said to arise by a simulation 
of the form of just and accurate perceptions. 
Accordingly, we shall most frequently speak 
of them as illusions of perception. 
In order to investigate the nature of any 
kind of error, it is needful to understand the- 
kind of knowledge it imitates, and so we 
must begin our inquiry into the nature of 
illusions of sense by a brief account of the 
psychology of perception ; and, in doing this,, 
we shall proceed best by regarding this oper- 
ation in its most complete form, namely, 
that of visual perception. 
I may observe that in this analysis of per- 
ception I shall endeavor to keep to known, 
facts, namely, the psychical phenomena or 
events which can be seen by the methods of 
scientific psychology to enter into the mental 
content called the percept. I do not now 
inquire whether such an analysis can help us- 
to understand all that is meant by perception. 
This point will have to be touched later on. 
Here it is enough to say that, whatever our 
philosophy of perception may be, we must 
accept the psychological fact that the con- 
crete mental state in the act of perception is; 
built up out of elements, the history of which, 
can be traced by the methods of mental sci- 
ence. 
Psychology of Perception.—Confining our- 
selves for the present to the mental, as dis- 
tinguished from the physical, side of the 
operation, we soon find that perception is 
not so simple a matter as it might at first 
seem to be. When a man on a hot day looks- 
at a running stream and “ sees ” the deli- 
cious coolness, it is not difficult to show that 
he is really performing an act of mental syn- 
thesis or imaginative construction. To the 
sense-impression* which his eye now gives- 
him, he adds something which past experi- 
ence has bequeathed to his mind. In per- 
ception, the materia] of sensation is acted 
on by the mind, which embodies in its pres- 
ent attitude all the results of its past growth. 
Let us look at' this process of synthesis a1 
little more closely. 
When a sensation arises in the mind, it 
may, under certain circumstances, go unat- 
tended to. In that case there is no percep- 
tion. The sensation floats in the dim outer 
regions of consciousness as a vague feeling, 
the real nature and history of which are 
unknown. This remark applies not only to- 
the undefined bodily sensations that are 
always oscillating about the threshold of 
CHAPTER III. 
ILLUSIONS OF PERCEPTION : GENERAL. 
The errors with which we shall be con- 
cerned in this chapter are those which are 
commonly denoted by the term illusion, that 
* It might even be urged that the order here 
adopted is scientifically he best, since sense-per- 
ception is the earliest form of knowledge, intro- 
spected facts being known only in relation to per- 
ceived facts. But if the mind's knowledge of its 
own states is thus later in time, it is earlier in the 
logical order, that is to say, it is the most strictly 
presentative form of knowledge. 
* Here and elsewhere I use the word “ impres- 
sion ” for the whole complex of sensation which is 
present at the moment. It may, perhaps, not be 
unnecessary to add that, in employing this term, I 
am making no assumption about the independent 
existence of external objects. A. PSYCHOLOGICAL STUDY. 
7 
«bseure consciousness, but to the higher 
sensation* connected with tne special organs 
of perception. The student in optics soon 
makes the startling discovery that his field 
of vision has all through his life been haunted 
with weird shapes which have never troubled 
the serenity of his mind just because they 
have never been distinctly attended to. 
The immediate result of this process of 
directing the keen glance of attention to a 
sensation is to give it greater force and dis- 
tinctness. By attending to it we discriminate 
it from other feelings present and past, and 
classify it with like sensations previously 
received. Thus, if I receive a visual im- 
pression of the color orange, the first conse- 
quence of attending to it is to mark it off 
from other color-impressions, including those 
of red and yellow. And in recognizing the 
peculiar quality of the impression by apply- 
ing to it the term orange, I obviously connect 
it with other similar sensations called by the 
same name. If a sensation is perfectly new, 
there cannot, of course, be this process of 
classifying, and in this case the closely 
related operation of discriminating it from 
other sensations is less exactly performed. 
But it is hardly necessary to remark that, in 
the mind of the adult, under ordinary circum- 
stances, no perfectly new sensation ever 
occurs. 
When the sensation, or complex sensation, 
is thus defined and recognized, there follows 
the process of interpretation, by which I 
mean the taking up of the impression as an 
element into the complex mental state known 
as a precept. Without going into the philo- 
sophical question of what this process of 
synthesis exactly means, I may observe that, 
by common consent, it takes place to a large 
extent by help of a reproduction of sensa- 
tions of various kinds experienced in the 
past. That is to say, the details in this act 
of combination are drawn from the store of 
mental recollections to which the growing 
mind is ever adding. In other words, the 
percept arises through a fusion of an actual 
sensation with mental representations or 
“ images ” of sensation.* Every element of 
the object that we thus take up in the act of 
perception, or put into the percept, as its 
actual size, distance, and so on, will be found 
to make itself known to us through mental 
images or revivals of past experiences, such 
as those we have in handling the object, 
moving to and from it, etc. It follows that 
if this is an essential ingredient in the act of 
perception, the process closely resembles an 
act of inference; and, indeed, Helmholtz dis- 
tinctly calls the perception of distance an un- 
conscious inference or a mechanically per- 
formed act of judgment. 
1 have hinted that these recovered sensa- 
tions include the feelings we experience in 
connection with muscular activity, a,s in 
moving our limbs, resisting or lifting heavy 
bodies, and walking to a distant object. 
Modern psychology refers the eye’s instanta- 
neous recognition of the most important ele- 
ments of an object (its essential or “ primary ” 
qualities) to a reinstatement of such simple 
experiences as these. It is, indeed, these 
reproductions which are supposed to consti- 
tute the substantial background of our per- 
cepts. 
Another thing worth noting with respect 
to this process of filling up a sense-impres- 
sion is that it draws on past sensations of 
the eye itself. Thus, when I look at the 
figure of an acquaintance from behind, my 
reproductive visual imagination supplies a 
representation of the impressions I am wont 
to receive when the more interesting aspect 
of the object, the front view, is present to 
my visual sense.* 
We may distinguish between different 
steps in the full act of visual recognition. 
First of all comes the construction of a 
material object of a particular figure and 
size, and at a particular distance ; that is to 
say, the recognition of a tangible thing 
having certain simple space-properties, and 
holding ascertain relation to other objects, 
and more especially our own body, in space. 
This is the bare perception of an object, 
which always takes place even in the case of 
perfectly new objects, provided they are seen 
with any degree of distinctness. It is to be 
added that the reference of a sensation of 
light or color to such an object involves the 
inclusion of a quality answering to the sensa- 
tion, as brightness, or blue color, in the thing 
thus intuited. 
This part of the process of filling in, which 
is the most instantaneous, automatic, and 
unconscious, may be supposed to answer to 
the most constant and therefore the most 
deeply organized connections of experience ; 
for, speaking generally, we never have an 
impression of color, except when there are cir- 
cumstances present which are fitted to yield 
us those simple muscular and tactual expe- 
riences through which the ideas of a particu- 
lar form, size, etc., are pretty certainly 
obtained. 
The second step in this process of present- 
ative construction is the recognition of an 
object as one of a class of things, for ex- 
ample, oranges, having certain special quali- 
ties, as a particular taste. In this step the 
Psychological usage has now pretty well substi- 
tuted the term “ image ” for “ idea,” in order to in- 
dicate an individual (as distinguished from a gen- 
eral) representation of a sensation or percept. It 
mi»ht, perhaps, be desirable to go further in this 
process of differentiating language, and to distin- 
guish between a sensational image, e.g. the repre- 
sentation of a color, and a perceptional image, as 
the representation of a colored object. It may be 
well to add that, in speaking of a fusion of an image 
and a sensation, I do not mean that the former 
exists apart for a single instant. The term “fu- 
sion” is used figuratively to describe the union of 
the two sides or aspects of a complete sensation. 
*This impulse to fill in visual elements not actu- 
ally present is strikingly illustrated in people’s diffi- 
culty in recognizing the gap in the field of vision 
answering to the insensitive “ blind ” spot on the 
retina. <Sre Helmholtz. Pkysiolngische C/>tik\ p. ILLUSIONS: 
connections of experience are less deeply or- 
ganized, and so we are able to some extent, 
by reflection, to recognize it as a kind of 
intellectual working up of the materials sup- 
plied us by the past. It is to be noted that 
this process of recognition involves a com- 
pound operation of classifying impressions 
as distinguished from that simple operation 
by which a single impression, such as a par- 
ticular color, is known. Thus the recogni- 
tion of such an object as an orange takes 
place by a rapid classing of a multitude of 
passive sensations of color, light, and shade, 
and those active or muscular sensations 
which are supposed to enter into the visual 
perception of form. 
A still less automatic step in the process 
of visual recognition is that of identifying in- 
dividual objects, as Westminster Abbey, or 
a friend, John Smith. The amount of ex- 
perience that is here reproduced may be very 
large, as in the case of recognizing a person 
with whom we have had a long and intimate 
acquaintance. t 
If the recognition of an object as one of a 
class, for example, an orange, involves a com- 
pound process of classing impressions, that 
of an individual object involves a still more 
complicated process. The identification of 
a friend, simple as this operation may at first 
appear, really takes place by a rapid classing 
of all the salient characteristic features which 
serve as the visible marks of that particular 
person. 
It is to be noted that each kind of recog- 
nition, specific and individual, takes place 
by a consciousness of likeness armd unlike- 
ness. It is obvious that a new individual 
object has characters not shared in by other 
objects previously inspected. Thus, we at 
once class a man with a dark-brown skin, 
wearing a particular garb, as a Hindoo, 
though he may differ in a host of particulars 
from the other Hindoos that we have ob- 
served. In thus instantly recognizing him 
as a Hindoo, we must, it is plain, attend to 
the points of similarity, and overlook for the 
instant the points of dissimilarity. In the 
case of individual identification, the same 
thing happens. Strictly speaking, no object 
ever appears exactly the same to us on two 
occasions. Apart from changes in the object 
itself, especially in the case of living beings, 
there are varying effects of illumination, of 
position in relation to the eve, of distance, 
and so on, which very distinctly affect the 
visual impression at different times. Yet 
the fact of our instantly recognizing a fa- 
miliar object in spite of these fluctuations of 
appearance, proves that we are able to over- 
look a very considerable amount of diversity 
when a certain amount of likeness is present. 
It is further to be observed that in these 
last stages of perception we approach the 
boundary line between perception and infer- 
ence. To recognize an object as one of a 
class is often a matter of conscious reflection 
and judgment, even when the class is con- 
stituted bv obvious materia] qualities which 
the senses may be supposed to apprehend im- 
mediately. Still more clearly does percep- 
tion pass into inference when the class is 
constituted by less obvious qualities, which 
require a careful and prolonged process of 
recollection, discrimination, and comparison, 
for their recognition. Thus, to recognize a 
man by certain marks of gesture and manner 
as a military man or a Frenchman, though 
popularly called a perception, is much more 
of an unfolded process of conscious inference. 
And what applies to specific recognition ap- 
plies still more forcibly to individual recog- 
nition, which is often a matter of very deli- 
cate conscious comparison and judgment. 
To say where the line should be drawn here 
between perception and observation on the 
one hand, and inference on the other, is clearly 
impossible. Our whole study of the illusions 
of perception will serve to show that the one 
shades off into the other too gradually to al- 
low of our drawing a hard and fast line be- 
tween them. 
Finally, it is to be noted that these last 
stages of perception bring us near the bound- 
ary line which separates objective experience 
as common and universal, and subjective or 
variable experience as confined to one or to 
a few. In the bringing of the object under a 
certain class of objects there is clearly room 
for greater variety of individual perception. 
For example, the ability to recognize a man 
as a Frenchman turns on a special kind of 
previous experience. And this transition 
from the common or universal to the indi- 
vidual experience is seen yet more plainly in 
the case of individual recognition. To ident- 
ify an object, say a particular person, com- 
monly presupposes some previous experience 
or knowledge of this object, and the exist- 
ence in the past of some special relation of 
the recognizer to the recognized, if only that 
of an observer. In fact, it is evident that in 
this mode of recognition we have the transi- 
tion from common perception to individual 
recollection.* 
While we may thus distinguish different 
steps in the process of visual recognition, we 
may make a further distinction, marking off 
a passive and an active stage in the process. 
The one may be called the stage of preper- 
ception, the other that of perception proper.t 
In the first the mind holds itself in a pas 
sive attitude, except in so far as the energies 
of external attention are involved. The im- 
pression here awakens the mental images 
which answer to past experiences according 
to the well-known laws of association. The 
interpretative image which is to transform 
the impression into a percept is now being 
formed by a mere process of suggestion. 
When the image is thus formed, the mind 
* This relation will be more fully discussed under 
the head of “ Memory.” 
11 adopt this distinction from Dr. J. Hughlings 
Jackson. See his articles, “On Affections of 
Speech from Diseases of the Brain,” in Brain, Nos. 
iii. and vii. The second stage might conveniently 
be named apperception, but for the special phi- 
losophical associations of the term. A PSYCHOLOGICAL STUDY. 
tnay be said to enter upon a more active stage, 
in which it now views the impression through 
the image, or applies this as a kind of mold 
or framework to the impression. This ap- 
pears to involve an intensification of the 
mental image, transforming it from a repre- 
sentative to a presentative mental state, mak- 
ing it approximate somewhat to the full in- 
tensity of the sensation. In many of our in- 
stantaneous perceptions these two stages are 
indistinguishable to consciousness. Thus, 
in most c’ses, the recognition of size, dis- 
tance, eti takes place so rapidly that it is 
impossible to detect the two phases here sep- 
arated. But in the classification of an ob- 
ject, or the identification of an individual 
thing, there is often an appreciable interval 
between the first reception of the impression 
and the final stage of complete recognition. 
And here it is easy to distinguish the two 
•stages of preperception and perception. The 
interpretative image is slowly built up by 
the operation of suggestion, at the close of 
which the impression is suddenly illumined 
as by a flash of light, and takes a definite, 
precise shape. 
Now, it is to be noted that the process of 
preperception will be greatly aided by any 
■circumstance that facilitates the construction 
of the particular interpretative image re- 
quired. Thus, the more frequently a simi- 
lar process of perception has been performed 
in the past, the more ready will the mind be 
to fall into the particular way of interpreting 
the impression. As G. H. Lewes well re- 
marks, “ The artist sees details where to 
other eyes there is a vague or confused mass; 
the naturalist sees arv animal where the ordi- 
nary eye only sees a form.” * This is but 
one illustration of the seemingly universal 
mental law, that what is repeatedly done will 
be done more and more easily. 
The process of preperception may be short- 
ened, not only by means of a permanent dis- 
position to frame the required interpretative 
scheme, the resictum of past like processes, 
but also by means of any temporary disposi- 
tion pointing in the same direction. If, for 
example, the mind of a naturalist has just 
been occupied about a certain class of bird, 
that is to say, if he has been dwelling on the j 
mental image of this bird, he will recognize 
one at a distance more quickly than he would 
otherwise have done. Such a simple mental 
operation as the recognition of one of the 
Jess common flowers, say a particular orchid, 
will vary in duration according as we have or 
have not been recently forming an image of 
this flower. The obvious explanation of this 
is that the mental image of an object bears 
a very close resemblance to the correspond- 
ing percept, differing from it, indeed, in de- 
gree only, that is to say, through the fact that 
it involves no actual sensation. Here again < 
we see illustrated a general psychological 
law, namely, that what the mind has recently 
, [ done, it tends (within certain limits) to go on 
i | doing. 
I | It is to be noticed, further, that the percep 
tion of a single object or event is rarely an 
isolated act of the mind. We recognize and 
understand the things that surround us 
through their relations one to another. Some- 
| times the adjacent circumstances and events 
suggest a definite expectation of the new 
impression. Thus, for example, the sound 
I of a gun heard during a walk in the country 
; is instantly interpreted by help of suggestions 
due to the previous appearance of the sports- 
! man, and the act of raising the gun to his 
j shoulder. It may be added that the verbal 
I suggestions of others act very much like the 
! suggestions of external circumstances. If I 
! am told that a gun is going to be fired, my 
! mind is prepared for it just as though I saw 
the sportsman * 
More frequently the effect of such sur- 
rounding circumstances is to give an air of 
i familiarity to the new impression, to shorten 
the interval in which the required interpre- 
tative image is forthcoming. Thus, when 
traveling in Italy, the visual impression an- 
i swering to a ruined temple or a bareheaded 
friar is construed much more rapidly than it 
would be elsewhere, because of the attitude 
of mind due to the surrounding circumstances. 
In all such cases the process of preperception 
connected with a given impression is effected 
more or less completely by the suggestions 
of other and related impressions. 
It follows from all that has been just said 
that our minds are never in exactly the same 
state of readiness with respect to a particular 
process of perceptional interpretation. Some- 
times the meaning of an impression flashes 
on us at once, and the stage of preperception 
becomes evanescent. At other times the 
same impression will fail for an appreciable 
interval to divulge its meaning. These dif- 
ferences are, no doubt, due in part to varia- 
tions in the state of attention at the moment; 
but they depend as well on fluctuations in 
the degree of the mind’s readiness to look at 
the impression in the required way. 
In order to complete this slight analysis of 
perception, we must look for a moment at its 
physical side, that is to say, at the nervous 
actions which are known or supposed with 
some degree of probability to accompany it. 
The production of the sensation is known 
to depend on a certain external process, 
namely, the action of some stimulus, as light, 
on the sense-organ, which stimulus has its 
point of departure in the object, such as it is 
conceived by physical science. The sensation 
arises when the nervous process is transmit- 
ted through the nerves to the conscious cen- 
ter, often spoken of as the sensorium, the 
exact seat of which is still a matter of some 
debate. 
The intensification of the sensation by the 
* Problems of Life and Mind, third series, p. io?. 
This writer employs the word “ preperception ” to 
denote this effect of previous perception. 
* Such verbal suggestion, moreover, acting 
through a sense-impression, has something of that 
vividness of effect which belongs to all excitation 
of mental images by external stimuli. ILLUSIONS: 
reaction of attention is supposed to depend 
on some re-enforcement of the nervous excita- 
tion in the sensory center proceeding from 
the motor regions, which are hypothetically 
regarded as the center of attention.* The 
classification of the impression, again, is 
pretty certainly correlated with the physical 
fact that the central excitation calls into activ- 
ity elements w'hich have already been excited 
in the same way. 
The nervous counterpart of the final stage 
of perception, the synthesis of the sensation 
and the mental representation, is not clearly 
ascertained. A sensation clearly resembles 
a mental image in quality. It is most obvi- 
ously marked off from the image by its greater 
vividness or intensity. Agreeably to this 
view, it is now held by a number of eminent 
physiologists and psychologists that the 
nervous process underlying a sensation oc- 
cupies the same central region as that which 
underlies the corresponding image. Accord- 
ing to this theory, the two processes differ in 
their degree of energy only, this difference 
being connected with the fact that the former 
involves, while the latter does not involve, 
the peripheral region of the nervous system. 
Accepting this view as on the whole well 
founded, I shall speak of an ideational, or 
rather an imaginational, and a sensational 
nervous process, and not of arrideational and 
a sensational center.! 
The special force that belongs to the rep- 
resentative element in a percept, as com- 
pared with that of a pure “ perceptional ” 
image,! is probably connected with the 
fact that, in the case of actual perception, 
the nervous process underlying the act of 
imaginative construction is organically united 
to the initial sensational process, of which 
indeed it may be regarded as a continuation. 
For the physical counterpart of the two 
stages in the interpretative part of percep- 
tion, distinguished as the passive stage of pre- 
perception, and the active stage of perception 
proper, we may, in the absence of certain 
knowledge, fall back on the hypothesis put 
forward by Dr. J. Hughlings Jackson, in the 
articles in Brain already referred to, namely, 
that the former answers to an action of 
the right hemisphere of the brain, the latter 
to a subsequent action of the left hemisphere. 
The expediting of the process of prepercep- 
tion in those cases where it has frequently 
been performed before, is clearly an illustra- 
tion of the organic law that every function is 
improved by exercise. And the temporary 
disposition to perform the process due to re- 
cent imaginative activity, is explained at once 
on the physical side by the supposition that 
an actual perception and a perceptional im- 
age involve the activity of the same nervous 
tracts. For, assuming this to be the case, it 
follows, from a well-known organic law, that 
a recent excitation would leave a temporary 
disposition in these particular structures to 
resume that particular mode of activity. 
What has here been said about visual 
perception will apply, mutatis mutandis, to 
other kinds. Although the eye is the organ 
of perception par excellence, our other senses 
are also avenues by which we intuit and rec- 
ognize objects. Thus touch, especially when 
it is finely' developed as it is in the blind, 
gives an immediate knowledge of objects—a 
more immediate knowledge, indeed, of their 
fundamental properties than sight. What 
makes the eye so vastly superior to the 
organ of touch as an instrument of percep- 
tion, is first of all the range of its action, 
taking in simultaneously a large number of 
impressions from objects at a distance as 
well as near; and secondly, though this may 
seem paradoxical, the fact that it gives us so 
much indirectly, that is, by way of associa- 
tion and suggestion. This is the interesting 
side of visual perception, that, owing to the 
vast complex of distinguishable sensations 
of light and color of various qualities and 
intensities, together with the muscular sensa- 
tions attending the varying positions of the 
organ, the eye is able to recognize at any 
instant a whole external world with its fun- 
damental properties and relations. The ear 
comes next to the eye in this respect, but 
only after a long interval, since its sensations 
(even in the case of musical combinations) 
do not simultaneously order themselves in 
an indefinitely large group of distinguishable 
elements, and since even the comparatively 
few sensations which it is capable of simul- 
taneously receiving, being altogether passive 
—that is to say, having no muscular accom- 
paniments—impart but little and vague in- 
formation respecting the exterpal order. It 
is plain, then, that in the study of illusion, 
where the indirectly known elements are the 
thing to be considered, the eye, and after 
this the ear, will mostly engage our attention.* 
* Touch gives much by way of interpretation 
only when an individual object, for example a 
man’s hat, is recognized by aid of this sense alone, 
in which case the perception distinctly involves 
the reproduction of a complete visual percept. I 
may add that the organ of smell comes next to that 
of hearing, with respect both to the range and 
definiteness of its simultaneous sensations, and to 
the amount of information furnished by these. A 
rough sense of distance as well as of direction is 
clearly obtainable by means of this organ. There 
seems to me no reason why an animal endowed 
with fine olfactory sensibility, and capable of an 
analytic separation of sense-elements, should not 
gain a rough perception of an external order much 
more complete than our auditory perception, which 
is necessarily so fragmentary. This supposition 
appears, indeed, to be the necessary complement 
to the idea first broached, so far as I am aware, 
by Professor Croom Robertson, that to such ani- 
mals, visual perception consists in a reference to a 
system of muscular feelings defined and bounded 
by strong olfactory sensations, rather than b* 
tactual sensations as in our case. 
* See Wundt, Physiologische Psychologic, p. 723. 
t For a confirmation of the view adopted in the 
text, see Professor'Bain, The Senses and the Intel- 
lect, Part II. ch. i. sec. 8 ; Herbert Spencer, Princi- 
ples of Psychology, vol. i. p. 234, et passim ; Dr. 
Ferrier, The Functions of the Brain, p. 258,et seq.; 
Professor Wundt, op. cit., pp. 644,645 ; G. H. Lewes 
Problems of Life and Mind, vol. v. p. 443, et seq. 
For an opposite view, see Dr. Carpenter, Mental 
Physiology, fourth edit., p.220, etc.; Dr. Maudsley, 
The Physiology of Mind, ch. v. p. 259, etc. 
X See note, p. 7. \ PSYCHOLOGICAL STUDY. 
So much it seemed needful to sav about 
the mechanism of perception, in order to 
understand the slight disturbances of this 
mechanism that manifest themselves in sense- 
illusion. It may be added that our study of 
these illusions will help still further to eluci- 
date the exact nature of perception. Nor- 
mal mental life, as a whole, at once illus- 
trates, and is illustrated by, abnormal. And 
while we need a rough provisional theorv of 
accurate perception in order to explain illu- 
sory perception at all, the investigation of 
this latter cannot fail to verify and even 
render more complete the theory which it 
thus temporarily adopts. 
Illusions of Perception.—With this brief 
psychological analysis of perception to help 
us, let us now pass to the consideration of 
the errors incident to the process, with a 
view to classify them according to their psy- 
chological nature and origin. 
And here there naturally arises the ques- 
tion, How shall we define an illusion of per- 
ception ? When trying to fix the definition 
of illusion in general, I practically disposed 
of this question. Nevertheless, as the point 
appears to me to be of some importance, I 
shall reproduce and expand one or two of 
the considerations then brought forward. 
It is said by certain philosophers that per- 
ception, as a whole, is an illusion, inasmuch 
as it involves the fiction of a real thing inde- 
pendent of mind, yet somehow present to it 
in the act of sense-perception. But this is a 
question for philosophy, not for science. 
Science, including psychology, assumes that 
in perception there is something real, with- 
out inquiring what it may consist of, or what 
its meaning may be. And though in the 
foregoing analysis of perception, viewed as a 
complex mental phenomenon or psychical 
process, I have argued that a percent gets 
its concrete filling up out of elements of con- 
scious experience or sensations, I have been 
careful not to contend that the particular ele- 
ments of feeling thus represented are the 
object of perception or the thing perceived. 
It may be that what we mean by a single 
object with its assemblage of qualities is 
much more than any number of such sensa- 
tions ; and it must be confessed that, on the 
face of it, it seems to be much more. And 
however this be, the question, What is meant 
by object; and is the common persuasion of 
the existence of such an entity in the act of 
perception accurate or illusory ? must be 
handed over to philosophy. 
While in the following examination of 
sense-illusions we put out of sight what cer- 
tain philosophers say about the illusoriness 
of perception as a whole, we shall also do 
well to leave out of account what physical 
science is sometimes supposed to tell us re- 
specting a constant element of illusion in 
perception. The physicist, by reducing all 
external changes to “ modes of motion,” 
appears to leave no room in his world-mech- 
anism for the secondary qualities of bodies, 
such as light and heat, as popularly con- 
ceived. Yet, while allowing this, I think we 
may still regard the attribution of qualities 
like color to objects as in the main correct 
and answering to a real fact. When a per- 
son says an object is red, he is understood 
by everybody as affirming something which 
is true or false, something therefore which 
either involves an external fact or is illu- 
sory. It would involve an external fact 
whenever the particular sensation which 
he receives -is the result of a physical action 
(ether vibrations of a certain order), which 
would produce a like sensation in anybody 
else in the same situation and endowed with 
the normal retinal sensibility. On the other 
hand, an illusory attribution of color would 
imply that there is no corresponding physi- 
cal agency at work in the case, but that the 
sensation is connected with exceptional indi- 
vidual conditions, as, for example, altered 
retinal sensibility. 
We are now, perhaps, in a position to 
frame a rough definition of an illusion of per- 
ception as popularly understood. A large 
number of such phenomena may be described 
as consisting in the formation of percepts or 
quasi-percepts in the minds of individuals 
under external circumstances which would 
not give rise to similar percepts in the case 
of other people. 
A little consideration, however, will show 
that this is not an adequate definition of 
what is ordinarily understood by an illusion 
of sense. There are special circumstances 
which are fitted to excite a momentary illu- 
sion in all minds. The optical illusions due 
to the reflection and refraction of light are 
not peculiar to the individual, but arise in all 
minds under precisely similar external con- 
ditions. 
It is plain that the illusoriness of a percep- 
tion is in these cases determined in relation 
to the sense-impressions of other moments 
and situations, or to what are 
better percepts than the present one. Some- 
times this involves an appeal from one sense 
to another. Thus, there is the process of 
verification of sight by touch, for example, 
in the case of optical images, a mode of per- 
ception which, as we have seen, gives a more 
direct cognition of external quality. Con- 
versely, there may occasionally be a reference 
from touch to sight, when it is a question of 
discriminating two points lying very close to 
one another. Finally, the same sense may 
correct itself, as when the illusion of the 
steroscope is corrected by afterward looking 
at the two separate pictures. 
We may thus roughly define an illusion of 
perception as consisting in the formation of 
a quasi-percept which is peculiar to an indi- 
vidual, or which is contradicted by another 
and presumably more accurate percept. Or, 
if we take the meaning of the word common 
to include both the universal as contrasted 
with the individual experience, and the per- 
manent, constant, or average, as distinguished 
from the momentary and variable percept, 
we may still briefly describe an illusion of 12 
1LLUSIONS: 
perception as a deviation from the common 
or collective experience. 
Sources of Sense-Illusion.—Understanding 
sense-illusion in this way, let us glance back 
at the process of perception in its several 
stages or aspects, with the object of discover- 
ing what room occurs for illusion. 
It appears at first as if the preliminary 
stages—the reception, discrimination, and 
classification of an impression—would not 
offer the slightest opening for error. This 
part of the mechanism of perception seems 
to work so regularly and so smoothly that 
one can hardly conceive a fault in the proc- 
ess. Nevertheless, a little consideration 
will show that even here all does not go on 
with unerring precision. 
Let us suppose that the very first step is 
wanting—distinct attention to an impression. 
It is easy to see that this will favor illusion 
by leading to a confusion of the impression. 
Thus the timid man will more readily fall 
into the illusion of ghost-seeing than a cool- 
headed observant man, because he is less 
attentive to the actual impression of the mo- 
ment. This inattention to the sense-impres- 
sion will be found to be a great co-operating 
factor in the production of illusions. 
But if the sensation is properly attended 
to, can there be error through a misappre- 
hension of what is actually in the mind at the 
.moment ? To say that there can may sound 
paradoxical, and yet in a sense this is demon- 
strable. I do not mean that there is an 
■ observant mind behind and distinct from the 
sensation, and failing to observe it accurately 
through a kind of mental short-sightedness. 
What I mean is that the usual psychical effect 
of the incoming nervous process may to 
-some extent be counteracted by a powerful 
reaction of the centers. In the course of our 
study of illusions, we shall learn that it 
is possible for the quality of an impression, 
as, for example, of a sensation of color, to be 
appreciably modified when there is a strong 
tendency to regard it in one particular way. 
Postponing the consideration of these, we 
may say that certain illusions appear clearly 
to take their start from an error in the proc- 
ess of classifying or identifying a present 
impression. On the physical side, we may 
say that the first stages of the nervous proc- 
ess, the due excitation of the sensory center 
in accordance with the form of the incoming 
stimulation and the central reaction involved 
in the recognition of the sensation, are in- 
complete. These are so limited and com- 
paratively unimportant a class, that it will be 
well to dispose of them at once. 
Confusion of the Sense-Impression.—The 
most interesting case of such an error is 
where the impression is unfamiliar and novel 
in character. I have already remarked that 
in the mental life of the adult perfectly new 
sensations never occur. At the same time, 
comparatively novel impressions sometimes 
arise. Parts of the sensitive surface of the 
body which rarely undergo stimulation are 
sometimes acted on, and at other times they 
receive partially new modes of stimulation. 
In such cases it is plain that the process of 
classing the sensation or recognizing it is not 
completed. It is found that whenever this 
happens there is a tendency to exaggerate 
the intensity of the sensation. The very fact 
of unfamiliarity seems to give to the sensa- 
tion a certain exciting character. As some- 
thing new and strange, it for the instant 
slightly agitates and discomposes the mind. 
Being unable to classify it with its like, we 
naturally magnify its intensity, and so tend 
to ascribe it to a disproportionately large 
cause. 
For instance, a light bandage worn about 
the body at a part usually free from pressure 
is liable to be conceived as a weighty mass. 
The odd sense of a big cavity in the mouth, 
which we experience just after the loss of a 
tooth, is probably another illustration of this 
principle. And a third example may also 
be supplied from the recollection of the den- 
tist’s patient, namely, the absurd imagina- 
tion which he tends to form as to what is 
actually going on in his mouth when a tooth 
is being bored by a modern rotating drill. 
It may be found that the same principle 
helps to account for the exaggerated impor- 
tance which we attach to the impressions of 
our dreams. 
It is evident that all indistinct impressions 
are liable to be wrongly classed. Sensations 
answering to a given color or form, are, 
when faint, easily confused with other sen- 
sations, and so an opening occurs for illu- 
sion. Thus, the impressions received from 
distant objects are frequently misinterpreted, 
and, as we shall see by and by, it is in this 
region of hazy impression that imagination 
is wont to play its most startling pranks. 
It is to be observed that the illusions 
arising from wrong classification will be 
more frequent in the case of those senses 
where discrimination is low. Thus, it is 
much easier in a general way to confuse two 
sensations of smell than two sensations ot 
color. Hence the great source of such errors 
is to be found in that mass of obscure sensa- 
tion which is connected with the organic 
processes, as digestion, respiration, etc., 
together with those varying tactual and motor 
feelings which result from what is called the 
subjective stimulation of the tactual nerves, 
and from changes in the position and condi- 
tion of the muscles. Lying commonly in 
what is known as the sub-conscious region 
of mind, undiscriminated, vague, and ill- 
defined, these sensations, when they come 
to be specially attended to, readily get mis- 
apprehended, and so lead to illusion, both in 
waking life and in sleep. I shall have occa- 
sion to illustrate this later on. 
With these sensations, the result of stimu- 
lations coming from remote parts of the or- 
ganism, may be classed the ocular impres- 
sions which we receive in indirect vision. 
When the eye is not fixed on an object, the 
impression, involving the activity of some 
peripheral region of the retina, is compara- A PSYCHOLOGICAL STUDY. 
tively indistinct. This will be much more 
the case when the object lies at a distance 
for which the eye is not at the time accom- 
modated. And in these circumstances, when 
we happen to turn our attention to the im- 
pression, we easily misapprehend it, and so 
fall into illusion. Thus, it has been re- 
marked by Sir David Brewster, in his Letters 
on Natural Magic (letter vii.), that when 
looking through a window at some object 
beyond, we easily suppose a fly on the win- 
dow-pane to be a larger object, as a bird, at 
a greater distance.* 
While these cases of a confusion or a 
wrong classification of the sensation are 
pretty well made out, there are other illu- 
sions or quasi-illusions respecting which it is 
doubtful whether they should be brought 
under this head. For example, it was found 
by Weber, that when the legs of a pair of 
compasses are at a certain small distance 
apart they will be felt as two by some parts 
of the tactual surface of the body, but only as 
one by other parts. How are we to regard 
this discrepancy ? Must we say that in the 
latter case there are two sensations, only 
that, being so similar, they are confused one 
with another? There seems some reason 
for so doing, in the fact that, by a repeated 
exercise of attention to the experiment, they 
may afterwards be recognized as two. 
We here come on the puzzling question, 
How much in the character of the sensation 
must be regarded as the necessary result of 
the particular mode of nervous stimulation 
at the moment, together with the laws of 
sensibility, and how much must be put down 
to the reaction of the mind in the shape of 
attention and discrimination ? For our 
present purpose we may say that, whenever 
a deliberate effort of attention does not suf- 
fice to alter the character of a sensation, this 
may be pretty safely regarded as a net 
result of the nervous process, and any error 
arising may be referred to the later stages 
of the process of perception. Thus, for 
example, the taking of the two points of 
a pair of compasses for one, where the 
closest attention does not discover the error, 
is best regarded as arising, not from a 
confusion of the sense-impression, but from 
a wrong interpretation of a sensation, occa- 
sioned by an overlooking of the limits of 
local discriminative sensibility. 
Misinterpretation of the Sense-Impression.— 
Enough has been said, perhaps, about those 
errors of perception which have their root in 
the initial process of sensation. We may 
now pass to the far more important class of 
illusions which are related to the later stages 
of perception, that is to say, the process of 
interpreting the sense-impression. Speaking 
generally, one .may describe an illusion of 
perception as a misinterpretation. The wrong 
kind of interpretative mental image gets 
combined with the impression, or, if with 
Helmholtz we regard perception as a process 
of “ unconscious inference,” we may say that 
these illusions involve an unconscious falla- 
cious conclusion. Or, looking at the phys- 
ical side of the operation, it may be said that 
the centra] course taken by the nervous proc- 
ess does not correspond to the external rela- 
tions of the moment. 
As soon as we inspect these illusions of 
interpretation, we see that the/ fall into two 
divisions, according as they are connected 
with the process of suggestion, that is to say, 
the formation of the interpretative image so 
far as determined by links of association 
with the actual impression, or with an inde- 
pendent process of preperception as explained 
above. Thus, for example, we fall into the 
illusion of hearing two voices when our 
shout is echoed back, just because the second 
auditory impression irresistibly calls up the 
image of a second shouter. On the other 
hand, a man experiences the illusion of see- 
ing specters of familiar objects just after 
exciting Ms imagination over a ghost-storyr 
because the mind is strongly predisposed to- 
frame this kind of percept. The first class- 
of illusions arises from without, the sense- 
impression being the starting-point, and the 
process of preperception being controlled by 
this. The second class arises rather from 
within, from an independent or spontaneous' 
activity of the imagination. In the one case 
the mind is comparatively passive; in the 
other it is active, energetically reacting on 
the impression, and impatiently anticipating 
the result of the normal process of preper- 
ception. Hence I shall, for brevity’s sake, 
commonly speak of them as Passive and 
Active Illusions.* 
I may, perhaps, illustrate these two classes- 
of illusion by the simile of an interpreter 
poring over an old manuscript. The first 
would be due to some peculiarity in the docu- 
ment misleading his judgment, the second to 
some caprice or preconceived notion in the 
interpreter’s mind. 
It is not difficult to define conjecturally 
the physiological conditions of these two 
large classes of illusion. On the physical 
side, an illusion of sense, like a just percep- 
tion, is the result of a fusion of the nervous 
process answering to a sensation with a nerv- 
ous process answering to a mental image. 
In the case of passive illusions, this fusion 
may be said to take place in consequence of 
some point of connection between the two. 
The existence of such a connection appears 
to be involved in the very fact of suggestion, 
and may be said to be the organic result of 
frequent conjunctions of the two parts of the 
* It may be —ii'T, perhaps, that th: exceptional 
direction of attention, by giving an inusual inten- 
sity to the impression, causes us to exaggerate it 
just as in the case of a novel sensation. An effort 
of attention directed to any of our vague bodily 
sensations easily leads us to magnify its cause. A 
similar confusion may arise even in direct vision, 
when the objects are looked at in a dim light, 
through a want of proper accommodation. (See 
Sir D. Brewster, op. cit.y letter i.) 
♦They might also be distinguished as objective 
and subjective illusions, or as illusions * posteriori 
and illusions a priori. 14 
ILLUSIONS: 
nervous operation in our past history. In 
the case of active illusions, however, which 
spring rather from the independent energy 
of a particular mode of the imagination, this 
point of organic connection is not the only 
or even the main thing. In many cases, as 
we shall see, there is only a faint shade of 
resemblance between the present impression 
and the mental image with which it is over- 
laid. The illusions dependent on vivid ex- 
pectation thus answer much less to an object- 
ive conjunction of past experiences than to 
a capricious subjective conjunction of mental 
images. Here, then, the fusion of nervous 
processes must have another cause. And it 
is not difficult to assign such a cause. The 
antecedent activity of imagination doubtless 
involves as its organic result a powerful 
temporary disposition in the nervous struct- 
ures concerned to go on acting. In other 
words, they remain in a state of sub-excita- 
tion, which can be raised to full excitation 
by a slight additional force. The more 
powerful this disposition in the centers in- 
volved in the act of imagination, the less the 
additional force of external stimulus required 
to excite them to full activity. 
Considering the first division, passive illu- 
sions, a little further, we shall see that they 
may be broken up into two sub-classes, ac- 
cording to the causes of the errors. In a 
general way we assume that the impression 
always answers to some quality of the object 
which is perceived, and varies with this; 
that, for example, our sensation of color in- 
variably represents the quality of external 
color which we attribute to the object. Or, 
to express it physically, we assume that the 
external force acting on the sense-organ in- 
variably produces the same effect, and that 
the effect always varies with the external 
cause. But this assumption, though true in 
the main, is not perfectly correct. It sup- 
poses that the organic conditions are constant 
and that the organic process faithfully reflects 
the external operation. Neither of these 
suppositions is strictly true. Although in 
general we may abstract from the organism 
and view the relation between the external 
fact and the mental impression as direct, we 
cannot always do so. 
This being so, it is possible for errors of 
perception to arise through peculiarities of 
the nervous organization itself. Thus, as I 
have just observed, sensibility has its limits, 
and these limits are the starting-point in a 
certain class of widely shared or common illu- 
sions. An example of this variety is the tak- 
ing of the two points of a pair of compasses 
for one by the hand, already referred to. 
Again, the condition of the nervous structures 
varies indefinitely, so that one and the same 
stimulus may, in the case of two individuals 
or of the same individual at different times, 
produce widely unlike modes of sensation. 
Such variations are clearly fitted to lead to 
gross individual errors as to the external 
cause of the sensation. Of this sort is the 
illusory sense of temperature which we often 
experience through a special state of the or- 
gan employed. 
While there are these errors of interpreta- 
tion due to some peculiarity of the organiza- 
tion, there are others which involve no such 
peculiarity, but arise through the speical 
character or exceptional conformation of the 
environment at the moment. Of this order 
are the illusions connected with the reflection 
of light and sound. We may, perhaps, dis- 
tinguish the first sub-class as organically 
conditioned illusions, and the second as extra- 
organically determined illusions. It may be 
added that the latter are roughly describable 
as common illusions. They thus answer in 
a measure to the first variety of organically 
conditioned illusions, namely, those connected 
with the limits of sensibility. On the other 
hand, the active illusions, being essentially 
individual or subjective, may be said to cor- 
respond to the other variety of this class— 
those connected with variations of sensibility. 
Our scheme of sense-illusions is now com- 
plete. First of all, we shall take up the 
passive illusions, beginning with those which 
are conditioned by special circumstances in 
the organism. After that we shall illustrate 
those .which depend on peculiar circumstan- 
ces in the environment. And finally, we 
shall separately consider what I have called 
the active illusions of sense. 
It is to be observed that these illusions of 
perception properly so called, namely, the 
errors arising from a wrong interpretation of 
an impression, and, not from a confusion of 
one impression with another, are chiefly illus- 
trated in the region of the two higher senses, 
sight and hearing. For it is here, as we have 
seen, that the interpretative imagination has 
most work to do in evolving complete per- 
cepts of material, tangible objects) having 
certain relations in space, out of a limited 
and homogeneous class of sensations, namely, 
those of light and color, and of sound. As 
I have before observed, tactual perception, 
in so far as it is the recognition of an object 
of a certain size, hardness, and distance from 
our body, involves the least degree of inter- 
pretation, and so offers little room for error; 
it is only when tactual perception amounts to 
the recognition of an individual object, clothed 
with secondary as well as primary qualities, 
that an opening for palpable error occurs. 
With respect, however, to the first sub- 
class of these illusions, namely, those arising 
from organic peculiarities which give a twist, 
so to speak, to the sensation, no very marked 
contrast between the different senses pre- 
sents itself. So that in illustrating this 
group we shall be pretty equally concerned 
with the various modes of perception con- 
nected with the different senses. 
It may be said once for all that in thus 
marking off from one another certain groups 
of illusion, I am not unmindful of the fact 
that these divisions answer to no very sharp 
natural distinctions. In fact, it will be found 
that one class gradually passbs into the 
other, and that the different characteristics \ PSYCHOLOGICAL STUD\ 
here separated often combine in a most per- 
plexing way. All that is claimed for this 
classification is that it is a convenient mode 
of mapping out the subject. 
respond to objective differences. For ex- 
ample, we tend to magnify the differences of 
light among objects, all of which are feebly 
illuminated, that is to say, to see them much 
more removed from one another in point of 
brightness than when they are more strongly 
illuminated. Helmholtz relates that, owing 
to this tendency, he has occasionally caught 
himself, on a dark night, entertaining the 
illusion that the comparatively bright objects 
visible in twilight were self-luminous.* 
Again, there are limits to the conscious 
separation of sensations which are received 
together, and this fact gives rise to illusion. 
In general, the number of distinguishable 
sensations answers to the number of external 
causes; but this is not always the case, and 
here we naturally fall into the error of mis- 
taking the number of the stimuli. Reference 
has already been made to this fact in connec- 
tion with the question whether consciousness 
can be mistaken as to the character of a 
present feeling. 
The case of confusing two impressions 
when the sensory fibers, involved are very 
near one another, has already been alluded 
to. Both in touch and in sight we always 
take two or more points for one when they 
are only separated by an interval that falls 
below the limits of local discrimination. It 
seems to follow from this that our perception 
of the world as a continuum, made up of 
points perfectly continuous one with another, 
may, for what we know, be illusory. Sup- 
posing the universe to consist of atoms sepa- 
rated by very fine intervals, then it is demon- 
strable that it would appear to our sensibility 
as a continuum, just as it does now.! 
Two or more simultaneous sensations are 
indistinguishable from one another, not only 
when they have nearly the same local origin, 
but under other circumstances. The blend- 
ing of partial sensations of tone in a klang- 
sensation, and the coalescence in certain 
cases of the impressions received by way of 
the two retinas, are examples of this. It is 
not quite certain what determines this fusion 
of two simultaneous feelings. It may be said 
generally that it is favored by similarity be- 
tween the sensations; } by a comparative 
feebleness of one of the feelings; by the fact 
of habitual concomitance, the two sensations 
occurring rarely, if ever, in isolation; and by 
the presence of a mental disposition to view 
them as answering to one external object. 
These considerations help us to explain the 
coalescence of the retinal impressions and 
CHATTER IV. 
ILLUSIONS of perception—continued. 
A. Passive Jllusions (a) as determined by 
the Organism.—In dealing with the illusions 
which are related to certain peculiarities in 
the nervous organism and the laws of sensi- 
bility, I shall commence with those which 
are connected with certain limits of sensi- 
bility. 
Limits of Sensibility.—To begin with, it is 
known that the sensation does not always 
answer to the external stimulus in its degree 
or intensity. Thus, a certain amount of 
stimulation is necessary before any sensation 
arises. And this will, of course, be greater 
when there is little or no attention directed 
to the impression, that is to say, no co-opera- 
ting central reaction. Thus it happens that 
slight stimuli go overlooked, and here illu- 
sion may have its starting-point. The most 
familiar example of such slight errors is that 
of movement. When we are looking at 
objects, our ocular muscles are apt to execute 
very slight movements which escape our no- 
tice. Hence we tend, under certain circum- 
stances, to carry over the retinal result of the 
movement, that is to say, the impression pro- 
duced by a shifting of the parts of the retinal 
image to new nervous elements, to the object 
itself, and so to transform a “ subjective ” 
into an “ objective ” movement. In a very 
interesting work on apparent or illusory 
movements, Professor Iloppe has fully inves- 
tigated the facts of such slight movements, 
and endeavored to specify their causes.* 
Again, even when the stimulus is sufficient 
to produce a conscious impression, the degree 
of the feeling may not represent the de- 
gree of the stimulus. To take a very incon- 
spicuous case, it is found by Fechner that a 
given increase of force in the stimulus pro- 
duces a less amount of difference in the re- 
sulting sensations when the original stimulus 
is a powerful one than when it is a feeble one. 
It follows from this, that differences in the 
degree of our sensations do not exactly cor- 
* Die Schein-Beiuegungen, von Professor Dr. J. 
I. Hoppe (1879); cf an ingenious article on “Opti- 
cal Illusions of Motion,” by Professor Silvanus P. 
Thompson, in Brain, October, 1880. These illu- 
sions frequently involve the co-operation of some 
preconception or expectation. For example, the 
apparent movement of a train when we are watch- 
ing it and expecting it to move, involves both an 
element of sense-impression and of imagination. 
It is possible that the illusion of table-turning 
rests on the same basis, the table-turner being un- 
aware of the fact of exerting a certain amount of 
muscular force, and vividly expecting a movement 
of the object. 
* Physiologische Optik, p. 316. 
+ It is plain that this supposed error could only 
be brought under our definition of illusion by ex- 
tending the latter, so as to include sense-perceptions 
which are contraditted by reason employing ideal- 
ized elements of sense-impression, which, as Lewes 
has shown (.Problems of Life and Mind, i. p. 260), 
make up the “ extra-sensible world ” of science. 
f An ingenious writer, M. Binet, has tried to 
prove that the fusion of homogeneous sensations, 
having little difference of local color, is an illus- 
tration of this principle. (See the Revue Philoso- 
phique, September, 1880.) 16 
ILLUSIONS: 
its limits, the fusion of partial tones, and so 
on.* 
It is plain that this fusion of sensations, 
whatever its exact conditions may be, gives 
rise to error or wrong interpretation of the 
sense-impression. Thus, to take the points 
of two legs of a pair of compasses for one 
point is clearly an illusion of perception. 
Here is another and less familiar example. 
Very cold and smooth surfaces, as those of 
metal, often appear to be wet. I never feel 
sure, after wiping the blades of my skates, 
that they are perfectly dry, since they always 
seem more or less damp to my hand. What 
is the reason of this ? Helmholtz explains 
the phenomenon by saying that the feeling 
we call by the name of wetness is a com- 
pound sensation consisting of one of tem- 
perature and one of touch proper. These 
sensations occurring together so frequently, 
blend into one, and so we infer, according to 
the general instinctive tendency already no- 
ticed, that there is one specific quality an- 
swering to the feeling. And since the feel- 
ing is nearly always produced by surfaces 
moistened by cold liquid, we refer it to this 
circumstance, and speak of it as a feeling of 
wetness. Hence, when the particular con- 
junction of sensations arises apart from this 
external circumstance, we erroneously infer 
its presence.! 
The most interesting case of illusion con- 
nected with the fusion of simultaneous sen- 
sations is that of single vision, or the deeply 
organized habit of combining the sensations 
of what are called the corresponding points 
of the two retinas. This coalescence of two 
sensations is so far erroneous since it makes 
us overlook the existence of two distinct ex- 
ternal agencies acting on different parts of 
the sensitive surface of the body. And this 
is the more striking in the case of looking at 
solid objects, since here it is demonstrable 
that the forces acting on the two retinas are 
not perfectly similar. Nevertheless, such a 
coalescence plainly answers to the fact that 
these external agencies usually arise in one 
and the same object, and this unity of the 
object is, of course, the all-important thing 
to be sure of. 
This habit may, however, beget palpable 
illusion in another way. In certain excep- 
tional cases the coalescence does not take 
place, as when I look at a distant object and 
hold a pencil just before my eyes * And in 
this case the organized tendency to take one 
visual impression for one object asserts its 
force, and I tend to fall into the illusion of 
seeing two separate pencils. If I do not 
wholly lapse into the error, it is because my 
experience has made me vaguely aware that 
double images under these circumstances 
answer to one object, and that if there were 
really two pencils present I should have four 
visual impressions. 
.Once more, it is a law of sensory stimula- 
tion that an impression persists for an appre- 
ciable time after the cessation of the action 
of the stimulus. This “ after sensation ” will 
clearly lead to illusion, in so far as we tend 
to think of the stimulus as still at work. It 
forms, indeed, as will be seen by and by, the 
simplest and lowest stage of hallucination. 
Sometimes this becomes the first stage of a 
palpable error. After listening to a child 
crying for some time the ear easily deceives 
itself into supposing that the noise is con- 
tinued when it has actually ceased. Again, 
after taking a bandage from a finger, the 
tingling and other sensations due to the 
pressure sometimes persist for a good time, 
in which case they easily give rise to an illu- 
sion that the finger is still bound. 
It follows from this fact of the reverbera- 
tion of the nervous structures after the re- 
moval of a stimulus, that whenever two dis- 
continuous stimulations follow one another 
rapidly enough, they will appear continuous. 
This fact is a fruitful source of optical illu- 
sion. The appearance of a blending of the 
stripes of colors on a rotating disk or top, of 
the formation of a ring of light by swinging 
round a piece of burning wood, and the illu- 
sion of the toy known as the thaumatrope, or 
wheel of life, all depend on this persistence 
of retinal impression. Many of the startling 
effects of sleight of hand are undoubtedly 
due in part to this principle. If two succes- 
sive actions or sets of circumstances to which 
the attention of the spectator is specially 
directed follow one another by a very narrow 
interval of time, they easily appear continu- 
ous, so that there seems absolutely no time 
for the introduction of an intermediate step.t 
There is another limit to sensibility which 
is in a manner the opposite to the one just 
named. It is a law of nervous stimulation 
that a continued activity of any structure 
results in less and less psychic result, and 
* Even the fusion of elementary sensations of 
color, on the hypothesis of Young and Helmholtz, 
in a seemingly simple sensation may be explained 
to some extent by these circumstances, more espe- 
cially the identity of local interpretation. 
t The perception of luster as a single quality 
seems to illustrate a like error. There is good rea- 
son to suppose that this impression arises through 
a difference of brightness in the two retinal images 
due to the regularly reflected light. And so when 
this inequality of retinal impression is imitated, as 
it may easily be by combining a black and a white 
surface in a stereoscope, we imagine that we are 
looking at one lustrous surface. (See Helmholtz, 
Physiologische Optik, p. 782, etc., and Populare 
ivissenscha/tliche Yortrdge, 2tes Heft, p. 80.) 
* The conditions of the production bf these 
double images have been accurately determined by 
Helmholtz, who shows that the coalescence of im- 
pressions takes place whenever the object is so situ- 
ated in the field of vision as to make it practically 
necessary that it should be recognized as one. 
t These illusions are, of course, due in part to 
inattention, since close critical scrutiny is often 
sufficient to dispel them. They are also largely pro- 
moted by a preconception that the event is going 
to happen in a particular way. But of this more 
further on. I may add that the late Professor 
Clifford has argued ingeniously against the idea of 
the world being a continuum, by extending this 
idea of the wheel of life. (See Lectures and 
Essays, i. p. 112, et seq.) A PSYCHOLOGICAL STUDY. 
17 
that when a stimulus is always at work it 
ceases in time to have any appreciable effect. 
The common illustration of this law is drawn 
from the region of sound. A constant noise, 
as of a mill, ceases to produce any conscious 
sensation. This fact, it is plain, may easily 
become the commencement of an illusion. 
Not only may we mistake a measure of noise 
for perfect silence,* we may misconceive the 
real nature of external circumstances by over- 
looking some continuous impression. 
Curious illustrations of this effect are found 
in optical illusions, namely, the errors we 
make respecting the movement of stationary 
objects after continued movement of the 
eyes. When, for example, in a railway car- 
riage we have for some time been following 
the (apparent) movement or objects, as trees, 
etc., and turn our eyes to an apparently sta- 
tionary object, as the carpet of the compart- 
ment, this seems to move in the contrary di- 
rection to that of the trees. Helmholtz’s ex- 
planation of this illusion is that when we sup- 
pose that we are fixing our eye on the carpet 
we are really continuing to move it over the 
surface by reason of the organic tendency, al- 
ready spoken of, to go on doing anything 
that has been done. But since we are una- 
ware of this prolonged series of ocular move- 
ments, the muscular feelings having become 
faint, we take the impression produced by 
the sliding of the picture over the retina to 
be the result of a movement of the object.t 
Another limit to our sensibility, which 
needs to be just touched on here, is known 
by the name of the. specific energy of the 
nerves. One and the same nerve-fiber al- 
ways reacts in a precisely similar way, what- 
ever the nature of the stimulus. Thus, when 
the optic nerve is stimulated in any manner, 
whether by light, mechanical pressure, or an 
electric current, the same effect, a sensation 
of light, follows.| In a usual way, a given 
class of nerve-fiber is only stimulated by one 
kind of stimulus. Thus, the retina, in ordi- 
nary circumstances, is stimulated by light. 
Owing to this fact, there has arisen a deeply 
organized habit of translating the impression 
in one particular way. Thus, I instinctively 
regard a sensation received by means of the 
optic nerve as one caused by light. 
Accordingly, whenever circumstances arise 
in which a like sensation is produced by 
another kind of stimulus, we fall into illusion. 
The phosphenes, or circles of light which 
are seen when the hinder part of the eye-ball 
is pressed, may be said to be illusory in so 
far as we speak of them as perceptions of 
light, thus referring them to the external 
physical agency which usually causes them. 
The same remark applies to those “subject- 
ive sensations,” as they are called, which are 
known to have as their physical cause sub- 
jective stimuli, consisting, in the case of 
sight, in varying conditions of the peripheral 
organ, as increased blood-pressure. Strictly 
speaking, such simple feelings as these ap- 
pear to be, involve an ingredient of false per- 
ception: in saying that we perceive light at 
all, we go beyond the pure sensation, inter- 
preting this wrongly. 
Very closely connected with this limitation 
of our sensibility is another which refeis to 
the consciousness of the local seat, or origin 
of the impression. This has so far its basis 
in the sensation itself as it is well known 
that (within the limits of local discrimination, 
referred to above) sensations have a particu- 
lar “local ” color, which varies in the case of 
each of the nervous fibers by the stimulation 
of which they arise.* But though this much 
is known through a difference in the sensi- 
bility, nothing more is known. Nothing can 
certainly be ascertained by a mere inspection 
of the sensation as to the distance the nerv- 
ous process has traveled, whether from the 
peripheral termination of the fiber or from 
some intermediate point. 
In a general way, we refer our sensations 
to the peripheral endings of the nerves con 
cerned, according to what physiologists have 
called “ the law of eccentricity.” Thus I am 
said to feel the pain caused by a bruise in the 
foot in the member itself. This applies also 
to some of the sensations of the special 
senses. Thus, impressions of taste are 
clearly localized in the corresponding peri- 
pheral terminations. 
With respect to the sense of smell, and 
still more to those of hearing and sight, 
where the impression is usually caused by an 
object at a distance from the peripheral organ, 
our attention to this external cause leads us 
to overlook in part the “bodily seat” of 
the sensation. Yet even here we are dimly 
aware that the sensation is received by way 
of a particular part of the sensitive surface, 
that is to say, by a particular sense-organ. 
Thus, though referring an odor to a distant 
flower, we perceive that the sensation of odor 
has its bodily ’origin in the nose. And even in 
the case of hearing and sight, we vaguely 
refer the impressions, as such, to the appro- 
* It is supposed that in the case of every sense- 
organ there is always some minimum forces of 
stimulus at work, the effect of which on our con- 
sciousness is nil. 
+ See Helmholtz, Physiologische Ofitik, p. 603. 
Helmholtz’s explanation is criticised by Dr. Hoppe, 
in the work already referred to (sec. vii.), though 
I cannot see that his own theory of these move- 
ments is essentially different. The apparent move- 
ment of objects in vertigo, or giddiness, is prob- 
ably due to the loss, through a physical cause, of 
the impressions made by the pressure of the fluid 
contents of the ear on the auditory fibers, by which 
the sense of equilibrium and of rotation is usually 
received. (See Ferrier, Functions of the Brain, 
pp. 60, 61.) 
11 do not need here to go into the question 
whether, as Johannes Mliller assumed, this is an 
original attribute of nerve-structure, or whether, 
as Wundt suggests, it is due simply to the fact that 
certain kinds of nervous fiber have, in the course 
of evolution, been slowly adapted to one kind of 
stimulus. 
* I here refer to what is commonly supposed to be 
the vague innate difference of sensation according 
to the local origin, before this is rendered precise, 
and added toby experience and association ILLUSIONS: 
priate sense-organ. There is, indeed, in 
these cases a. double local reference, a faint 
one to the peripheral organ which is acted 
on, and a more distinct one to the object or 
the force in the environment which acts on 
this. 
Now, it may be said that the act of locali- 
zation is in itself distinctly illusory, since it 
is known that the sensation first arises in 
connection with the excitation of the sensory 
center, and not of the peripheral fiber* Yet 
it must at least be allowed that this localiza- 
tion of sensation answers to the important 
fact that, under usual circumstances, the 
agency producing the sensation is applied at 
this particular point of the organism, the 
knowledge of which point is supposed by 
modern psychologists to have been very 
slowly learnt by the individual and the race, 
through countless experiments with the mov- 
ing organ of touch, assisted by the eye. 
Similarly, the reference of the impression, 
in the case of hearing and sight, to an object 
in the environment, though, as we have seen, 
Yom one point of view illusory, clearly an- 
swers to a fact of our habitual experience; 
for in an immense preponderance of cases at 
least a visual or auditory impression does 
arise through the action on the sense-organ 
of a force (ether or air waves) proceeding 
from a distant object. 
In some circumstances, however, even this 
element of practical truth disappears, and the 
localization of the impression, both within 
and without the organism, becomes altogether 
illusory. This result is involved in the illu- 
sions, already spoken of, which arise from 
the instinctive tendency to refer sensations 
to the ordinary kind of stimulus. Thus, 
when a feeling resulting from a disturbance 
in the optic nerve is interpreted as one of 
external light vaguely felt to be acting on the 
eye, or one resulting from some action set up 
in the auditory fiber as a sensation of external 
sound vaguely felt to be entering the ear, we 
see that the error of localization is a conse- 
quence of the other error already character- 
ized. 
As I have already observed, an excitation 
of a nerve at any other point than the peri- 
pheral termination, occurs but rarely in nor- 
mal life. One familiar instance is the stimu- 
lation of the nerve running to the hand and 
fingers, by a sharp blow on the elbow over 
which it passes. As everybody knows, this 
gives rise to a sense of pain at the extremities 
of the nerve. The most common illustration 
of such errors of localization is found in sub- 
jective sensations, such as the impression we 
sometimes have of something creeping over 
the skin, of a disagreeable taste in the mouth, 
of luminous spots floating across the field of 
vision, and so on. The exact physiological 
seat of these is often a matter of conjecture 
only; yet it may safely be said that in many 
instances the nervous excitation originates 
at some point considerably short of its peri- 
pheral extremity: in which case there occurs 
the illusion of referring the impressions to* 
the peripheral sense-organ, and to an external 
force acting on this. 
The most striking instances of these errors 
of localization are found in abnormal circum- 
stances. It is well known that a man who 
has lost a leg refers all sensations arising 
from a stimulation of the truncated fibers to 
his lost foot, and in some cases has even to 
convince himself of the non-existence of his 
lost member by sight or touch. Patients 
often describe these experiences in very odd 
language. “ If,” says one of Ur. Weir Mitch- 
ell’s patients, “ I should say I am more sure 
of the leg which ain’t than the one which air, 
I guess I should be about correct.” * 
There is good reason for supposing that 
this source of error plays a prominent part 
in the illusions of the insane. Diseased 
centers may be accompanied by disordered 
peripheral structures, and so subjective sen- 
sation may frequently be the starting-point 
of the wildest illusions. Thus, a patient’s 
horror of poison may have its first origin in 
some subjective gustatory sensation. Simi- 
larly, subjective tactual sensations may give 
rise to gross illusions, as when a patient 
“ feels ” his body attacked by foul and de- 
structive creatures. 
It may be well to remark that this mis- 
taken interpretation of the seat or origin of 
subjective sensation is closely related to 
hallucination. In so far as the error involves 
the ascription of the sensation to a force ex- 
ternal to the sense-organ, this part of the 
mental process must, when there is no such 
force present, be viewed as hallucinatory. 
Thus, the feeling of something creeping over 
the skin is an hallucination in the sense that 
it implies the idea of an object external to 
the skin. Similarly, the projection of an 
ocular impression due to retinal disturbance 
into the external field of vision, may rightly 
be named an hallucination. But the case is 
not always so clear as this. Thus, for exam- 
ple, when a gustatory sensation is the result 
of an altered condition of the saliva, it may 
be said that the error is as much an illusion 
as an hallucination.f 
In a wide sense, again, all errors connected 
with those subjective sensations which arise 
from a stimulation of the peripheral regions 
* The illusory character of this simple mode of 
perception is seen best, perhaps, in the curious 
habit into which we fall of referring a sensation of 
contact or discomfort to the edge of the teeth, the 
hair, and the other insentient structures, and even 
to anything customarily attached to the sentient 
surface, as dress, a pen, graving tool, etc. Cn 
these curious illusions, see Lotze, Mikrokosmusy 
third edit., vol. ii. p. 202, etc. ; Taine, De VIntelli- 
gence, tom. ii. p. S3, ct seq. 
* Quoted by G. H. Lewes, Problems of Life and 
Mindy third series, p. 335. These illusions are 
supposed to involve an excitation of the nerve- 
fibers (whether sensory or motor) which run to the 
muscles and yield the so-called muscular sensations. 
t It is brought out bv Griesinger (loc. cit.) and 
the other writers on the pathology of illusion 
already quoted, that in the case of subjective sen- 
sations of touch, taste, and smell, no sharp line can 
be drawn between illusion and hallucination. A PSYCHOLOGICAL STUDY. 
19 
of the nerve may be called illusions rather 
than hallucinations. Or, if they must be 
called hallucinations, they may be distin- 
guished as “peripheral” from those “cen- 
tral ” hallucinations which arise through an 
internal automatic excitation of the sensory 
•center. It is plain from this that the region 
of subjective sensation is an ambiguous 
region, where illusion and hallucination mix 
and become confused. To this point I shall 
have occasion to return by and by. 
I have now probably said enough respect- 
ing the illusions that arise through the fact of 
there being fixed limits to our sensibility. 
The rationale of these illusions is that when- 
ever the limit is reached, we tend to ignore it 
and to interpret the impression in the custo- 
mary way. 
Variations of Sensibility.—We will now 
pass to a number of illusions which depend 
on something variable in the condition of 
our sensibility, or some more or less excep- 
tional organic circumstance. These varia- 
tions may be momentary and transient or 
comparatively permanent. The illusion 
arises in each case from our ignoring the va- 
riation, and treating a given sensation under 
all circumstances as answering to one object- 
ive cause. 
First of all, the variation of organic state 
may effect our mental representation of the 
strength of the stimulus or external cause. 
Here the fluctuation may be a temporary or 
a permanent one. The first case is illustrated 
in the familiar example of taking a rooih to 
be brighter than it is when emerging from a 
dark one. Another striking example is that 
of our sense of the temperature of objects, 
which is known to be strictly relative to a 
previous sensation, or more correctly to the 
momentary condition of the organ. Yet, 
though every intelligent person knows this, 
the deeply rooted habit of making sensation 
the measure of objective quality asserts its 
sway, and frequently leads us into illusion. 
The well-known experiment of first plunging 
one hand in cold water, the other in hot, and 
then dipping them both in tepid, is a start- 
ling example of this organized tendency. 
For here we are strongly disposed to accept 
the palpable contradiction that the same 
water is at once warm and cool. 
Far more important than these temporary 
fluctuations of sensibility are the permanent 
alterations. Excessive fatigue, want of proper 
nutrition, and certain poisons are well known 
to be causes of such changes. They appear 
most commonly under two forms, exalted 
sensibility, or hyperaesthesia, and depressed 
sensibility, or anaesthesia. In these condi- 
tions flagrant errors are made as to the real 
magnitude of the causes of the sensations. 
These variations may occur in normal life 
to some extent. In fairly good health we 
experience at times strange exaltations of 
tactual sensibility, so that a very slight stimu- 
lus, such as the contact of the bed-clothes, 
becomes greatly exaggerated 
In diseased states of the nervous svstem 
these variations of sensibility become much 
more striking. The patient who has hyper- 
aesthesia fears to touch a perfectly smooth 
surface, or he takes a knock at the door to 
be a clap of thunder. The hypochondriac 
may, through an increase of organic sensi- 
bility, translate organic sensations as the 
effect of some living creature gnawing at his 
vitals. Again, states of anaesthesia lead to 
odd illusions among the insane. The com- 
mon supposition that the body is dead, or 
made of wood or of glass, is clearly refera- 
ble in part to lowered sensibility of the or- 
ganism.* 
It is worth adding, perhaps, that these 
variations in sensibility give rise not only 
to sensory but also to motor illusions. To 
take a homely instance, the last miles of a 
long walk seem much longer than the first, 
not only because the sense of fatigue leading 
us to dwell on the transition of time tends to 
magnify the apparent duration, but because 
the fatigued muscles and connected nerves 
yield a new set of sensations which constitute 
an exaggerated standard of measurement. 
A number of optical illusions illustrate the 
same thing. Our visual sense of direction is 
determined in part by the feelings accompany- 
ing the action of the ocular muscles, and so 
is closely connected with the perception of 
movement, which has already been touched 
on. If an ocular muscle is partially para- 
lyzed it takes a much greater “ effort ” to ef- 
fect a given extent of movement than when 
the muscle is sound. Hence any movement 
performed by the eye seems exaggerated. 
Hence, too, in this condition objects are seen 
in a wrong direction; for the patient reasons 
that they are where they would seem to be if 
he had executed a wider movement than he 
really has. This may easily be proved bv 
asking him to try to seize the object with 
his hand. The effect is exaggerated when 
complete paralysis sets in, and no actual 
movement occurs in obedience to the impulse 
from within.t 
Variations in the condition of the nerve 
affect not only the degree, but also the quality 
of the sensation, and this fact gives rise to a 
new kind of illusion. The curious phenomena 
of color-contrast illustrate momentary altera- 
tions of sensibility. When, after looking at 
a green color for a time, I turn my eye to a 
gray surface and see this of the complement- 
ary rose-red hue, the effect is supposed to 
be due to a temporary fatigue of the retina in 
relation to those ingredients of the total 
light in the second case which answer to 
* For a fuller account of these pathological dis- 
turbances of sensibility, see Griesinger; also Dr. 
A. Mayer, Die Sinnestauschungen. 
t Helmholtz, op. cit., p. 600, et seq. These facts 
seem to point to the conclusion that at least some 
of the feelings by which we know that we are ex- 
pending muscular energy are connected with the 
initial stage of the outgoing nervous process in 
the motor centers. In other pathological conditions 
,the sense of weight by the muscles of the arms 
is similarly confused. 20 
ILLUSIONS: 
the partial light in the first (the green 
rays).* 
These momentary modifications of sensi- 
bility are of no practical significance, being 
almost instantly corrected. Other modifica- 
tions are more permanent. It was found by 
Himly that when the retina is over-excitable 
every stimulus is raised in the spectrum scale 
of colors. Thus, violet becomes red. An 
exactly opposite effect is observed when the 
retina is torpid.t Certain poisons are known 
to affect the quality of the color-impression. 
Thus, santonin, when taken in any quantity, 
makes all colorless objects look yellow. 
Severe pathological disturbances are known 
to involve, in addition to hyperaesthesia and 
anaesthesia, what has been called paraesthesia, 
that is to say, that condition in which the 
quality of sensation is greatly changed. 
Thus, for example, to one in this state all 
food appears to have a metallic taste, and so 
on. 
If we now glance back at the various groups 
of illusions just illustrated, we find that they 
all have this feature in common : they depend 
on the general mental law that when we have 
to do with the unfrequent, the unimportant,, 
and therefore unattended to, and the excep- 
tional, we employ the ordinary, the familiar, 
and tbe well-known as our standard. Thus, 
whether we are dealing with sensations that 
fall below the ordinary limits of our mental 
experience, or with those which arise in 
some exceptional state of the organism, we 
carry the habits formed ;n the much wider 
region of average every-day perception with 
us. In a word, illusion in these cases always 
arises through what may, figuratively at least, 
be described as the application of a rule, 
valid for the majority of cases, to an excep- 
tional case. 
In the varieties of illusion just considered, 
the circumstance that gives the peculiarity 
to the case thus wrongly interpreted has 
been referred to the organism. In the illu- 
sions to which we now pass, it will be re- 
ferred to the environment. At the same 
time, it is plain that there is no very sharp 
distinction between the two classes. Thus, 
the visual illusion produced by pressing the 
eyeball might be regarded not only as the re- 
sult of the' organic law of the “specific 
energy ” of the nerves, but, with almost 
equal appropriateness, as the* consequence 
of an exceptional state of things in the en- 
vironment, namely, the pressure of a body 
on the retina. As I have already observed, 
the classification here adopted is to be viewed 
simply as a rough expedient for securing 
something like a systematic review of the 
phenomena. 
CHAPTER V. 
ILLUSIONS' OF PERCEPTION—continued. 
A. Passive Illusions (b) as determitied by tke 
Environment.—In the following groups of il- 
lusion we may look away from nervous proc- 
esses and organic disturbances, regarding the 
effect of any external stimulus as character- 
istic, that is, as clearly marked off from the 
effects of other'stimuli, and as constant for 
the same stimulus. The source of the illu- 
sion will be looked for in something excep- 
tional in the external circumstances, whereby 
one object or condition of an object imitates 
the effect of another object or condition, to 
which, owing to a large preponderance of ex- 
perience* we at once refer it. 
Exceptional Relation of Stimulus to Organ. 
—A transition from the preceding to the fol- 
lowing class of illusions is to be met with in 
those errors which arise from a very excep- 
tional relation between the stimulus and the 
organ of sense. Such a state of things is 
naturally interpreted by help of more com- 
mon and familiar relations, and so error 
arises. 
For example, we may grossly misinterpret 
the intensity of a stimulus under certain cir- 
cumstances. Thus, when a man crunches a 
biscuit, he has an uncomfortable feeling that 
the noise as of all the structures of his head 
being violently smashed is the same to other 
ears, and he may even acton his illusory 
perception, by keeping at a respectful distance 
from all observers. And even though he be 
a physiologist, and knows that the force of' 
sensation in this case is due to the propaga- 
tion of vibrations to the auditory center by 
other channels than the usual one of the ear, 
the deeply organized impulse to measure the 
strength of an external stimulus by the inten- 
sity of the sensation asserts its force. 
Again, if we turn to the process of percep- 
tional construction properly so called, the 
reference of the sensation to a material 
object lying in a certain direction, etc., we 
find a similar transitional form of illusion. 
The most interesting case of this in visual 
perception is that of a disturbance or dis- 
placement of the organ by external force. 
For example, an illusory sense of direction 
arises by the simple action of closing one 
eye, say the left, and pressing the other eye- 
ball with one of the fingers a little outwards, 
that is to the right. The result of this move- 
ment is, of course, to transfer the retinal 
picture to new nervous elements Lrther to 
* Wundt (Physiologische Psychologies p.653) would 
exclude from illusions all those errors of sense-per- 
ception which have their foundation in the normal 
structure and function of the organs of sense. 
Thus, he would exclude the effects of color-con- 
trast, e.gthe apparent modification of two colors 
in juxtarosition toward their common boundary, 
which probably arises (according to E. Hering) from 
some mutual influence of the temporary state of ac- 
tivity of adjacent retinal elements. Tome, however, 
these appear to be illusions, since they may be 
brought under the head of wrong interpretations 
of sense-impressions. When we see a gray patch 
as rose-red, as though it were so independently of 
the action of the complementary light previously 
or simultaneously, that is to say, as though it would 
appear rose-red to an eye independently of this ac- 
tion. we surely misinterpret. 
+ Quoted by G. H. Lewes, toe. cit., p. 3-57. A PSYCHOLOGICAL STUDY. 
21 
the right. And since, in this instance, the 
displacement is not produced in the ordinary 
way by the activity of the ocular muscle 
making itself known by certain feelings of 
movement, it is disregarded altogether, and 
the direction of the objects is judged as 
though the eye were stationary. 
A somewhat similar illusion as to direc- 
tion occurs in auditory perception. The 
sense of direction by the ear is known to be 
due in part to the action of the auricle, or 
projecting part of the ear. This collects the 
air-waves, and so adds to the intensity of the 
sounds, especially those coming from in front, 
and thus assists in the estimation of direc- 
tion. This being so, if an artificial auricle 
is placed in front of the ears; if, for example, 
the two hands are each bent into a, sort of 
auricle, and placed in front of the ears, the 
back of the hand being in front, the sense of 
direction (as well as of distance) is confused. 
Thus, sounds really traveling from a point in 
front of the head will appear to come from 
behind it. 
Again, the perception of the unity of an 
object is liable to be falsified by the intro- 
duction of exceptional circumstances into 
the sense-organ. This is illustrated in the 
well-known experiment of crossing two fin- 
gers, say the third and fourth, and placing a 
marble or other small round object between 
them. Under ordinary circumstances, the 
two lateral surfaces (that is, the outer sur- 
faces of the two fingers) now pressed by the 
marble, can only be acted on simultaneously 
by two objects having convex surfaces. Con- 
sequently, we cannot help feeling the pres- 
ence of two objects in this exceptional 
instance. The illusion is analogous to that 
of the stereoscope, to be spoken of pres- 
ently 
Exceptional External A rrangements.— 
Passing now to those cases where the excep- 
tional circumstance is altogether exterior to 
the organ, we find a familiar example in the 
illusions connected with the action of well- 
known physical forces, as the refraction of 
light, and the reflection of light and sound. 
A stick half-immersed in water always looks 
broken, however well we may know that the 
appearance is due to the bending of the rays 
-of light. Similarly, an echo always sounds 
as though it came from some object in the 
direction in which the air-waves finally travel 
to the ear, though we are perfectly sure that 
these undulations have taken a circuitous 
course. It is hardly necessary to remind the 
reader that the deeply organized tendency to 
mistake the direction of the visible or audible 
object in these cases has from remote ages 
been made use of as a means of popular de- 
lusion. Thus, we are told by Sir 1). Brews- 
ter, in his entertaining Letters on Natural 
Magic (letter iv.), that the concave mirror 
was probably used as the instrument for 
bringing the gods before the people. The 
throwing of the images formed by such mir- 
rors upon smoke or against fire, so as to 
make them more distinct, seems to have 
been a tavorite device in the ancient art of 
necromancy. 
Closely connected with these illusions of 
direction with respect to resting objects, are 
those into which we are apt to fall respect- 
ing the movements of objects. What looks 
like the movement of something across the 
field of vision is made known to us either 
by the feeling of the ocular muscles, if the 
eye follows the object, or through the se- 
quence of locally distinct retinal impressions, 
if the eye is stationary. Now, either of these 
effects may result, not only from the actual 
movement of the object in a particular direc- 
tion, but from our own movement in an op- 
posite direction; or, again, from our both 
moving in the first direction, the object more 
rapidly than ourselves; or, finally, from our 
both moving in an opposite direction to this, 
ourselves more rapidly than the object. 
There is thus always a variety of conceivable 
explanations, and the action of past experi- 
ence and association shows itself very plainly 
in the determination of the direction of in- 
terpretation. Thus, it is our instinctive tend- 
ency to take apparent movement, for real 
movement, except when the fact of our own 
movement is clearly present to consciousness, 
as when we are walking, or when we are sit- 
ting behind a horse whose movement we see. 
And so when the sense of our own movement 
becomes indistinct, as in a railway carriage, 
we naturally drift into the illusion that ob- 
jects, such as trees, telegraph posts, and so 
on, are moving, when they are perfectly still. 
Under the same circumstances, we are apt to 
suppose that a train which is just shooting 
ahead of us is moving slowly. 
Similar uncertainties arise with respect to 
the relative movement of two objects, the eye 
being supposed to be fixed in space. When 
two objects seem to pass one another, it may 
be that they are both moving in contrary di- 
rections, or that one only is moving, or finally, 
that both are moving in the same direction, 
the one faster than the other. Experience 
and habit here again suggest the interpreta- 
tion which is most easy, and not unfrequently 
produce illusion. Thus, when we watch 
clouds scudding over the face of the moon, 
the latter seems moving rather than the for- 
mer, and the illusion only disappears when 
we fix the eye on the moon and recognize 
that it is really stationary. The probable 
reason of this is, as Wundt suggests, that 
experience has made it far easier for us to 
think of small objects like the moon moving 
rapidly, than of large masses like the clouds * 
The perception of distance, still more than 
that of direction, is liable to be illusory. In- 
deed, the visual recognition of distance, to- 
gether with that of solidity, has been the 
great region for the study of “ the deceptions 
* The subject of the perception of movement is too 
intricate to be dealt with fully here. I have only 
touched on it so far as necessary to illustrate our 
general principle. For a fuller treatment of the 
subject, see the work of Dr. Hoppe, already re- 
ferred to. 22 
ILLUSIONS: 
of the senses.” Without treating the subject 
fully here, I shall try to describe briefly the 
nature and source of these illusions.* 
Confining ourselves first of all to near ob- 
jects, we know that the smaller differences 
of distance in these cases are, if the eyes are 
at rest, perceived by means of the dissimilar 
pictures projected on the two retinas; or if 
they move, by this means, together with the 
muscular feelings that accompany different 
degrees of convergence of the two eyes. This 
was demonstrated by the famous experiments 
of Wheatstone. Thus, by means of the now 
familiar stereoscope, he was able to produce 
a perfect illusion of relief. The stereoscope 
may be said to introduce an exceptional state 
of things into the spectator’s environment. 
It imitates, by means of two flat drawings, 
the dissimilar retinal pictures projected by a 
single solid receding object, and the lenses 
through which the eyes look are so construct- 
ed as to compel them to converge as though 
looking on a single object. And so powerful 
is the tendency to interpret this impression 
as one of solidity, that even though we are 
aware of the presence of the stereoscopic 
apparatus, we cannot help seeing the two 
drawings as a single solid object. 
In the case of more remote objects, there 
is no dissimilarity of the retinal pictures or 
feelings of convergence to assist the eye in 
determining distance. Here its judgment, 
which now becomes more of a process of 
conscious inference, is determined by a number 
of circumstances which, through experience 
and association, have become the signs of 
differences of depth in space. Among these 
are the degree of indistinctness of the im- 
pression, the apparent or retinal magnitude 
(if the object is a familiar one), the relations 
of linear perspective, as the interruption of 
the outline of far objects by that of near ob- 
jects, and so on. In a process so complicated 
there is clearly ample room for error, and 
wrong estimates of distance whenever unusual 
circumstances are present are familiar to all. 
Thus the inexperienced English tourist, when 
in the clear atmosphere of Switzerland, where 
the impressions from distant objects are 
more distinct than at home, naturally falls 
into the illusion that the mountains are much 
nearer than they are, and so fails to realize 
their true altitude. 
Illusions of Art.—The imitation of solidity 
and depth by art is a curious and interesting 
illustration of the mode of production of illu- 
sion. Here we are not, of course, concerned 
with the question how far illusion is desirable 
in art, but only with its capabilities of illusory 
presentment; which capabilities, it may be 
added, have been fully illustrated in the 
history of art. The full treatment of this 
subject would form a chapter in itself; here 
I can only touch on its main features. 
Pictorial art working on a flat surface 
cannot, it is plain, imitate the stereoscope,, 
and produce a perfect sense of solidity. Yet 
it manages to produce a pretty strong illu- 
sion. It illustrates in a striking manner the 
ease with which the eye conceives relations 
of depth or relief and solidity. If, for ex- 
ample, on a carpet, wall-paper, or dress, 
bright lines are laid on a dark color as 
ground, wq -easily imagine that they are 
advancing. The reason of this seems to be 
that in out daily experience advancing sur- 
faces catch and reflect the light, whereas 
retiring surfaces are in shadow.* 
The same principle is illustrated in one of 
the means used by the artist to produce a 
strong sense of relief, namely, the cast 
shadow. A circle drawn with chalk with a 
powerful £ast shadow on one side will, with- 
out any shading or modeling of the form,, 
appear to stand out from the paper, thus n 
The reason is that the presence of such a' 
shadow so forcibly suggests to the mind that 
the object is a prominent one intervening 
between the light and the shaded surfaced 
Even without differences of light and 
shade, by a mere arrangement of lines, we 
mav produce a powerful sense of relief or 
solidity. A striking example of this is the 
way in which two intersecting lines some- 
times appear to recede from the eye, as the 
lines a a', b b', in the next drawing, which 
seem to belong to a regular pattern on the 
ground, at which the eye is looking from 
above and obliquely. 
Again, the correct delineation of the pro- 
jection of a regular geometrical figure, as a 
cube, suffices to give the eye a sense of relief. 
Fig. i. 
* Painters are well aware that the colors at the 
red end of the spectrum are apt to appear as 
advancing, while those of the violet end are known 
as retiring. The appearance of relief given by a 
gilded pattern on a dark blue as ground, is in part 
referable to the principle just referred to. In 
addition, it appears to involve a difference in the 
action of the muscles of accommodation in the suc- 
cessive adaptations of the eye to the most refran- 
gible and the least refrangible rays. (See Briicke,. 
Die Physiologic der Far her, sec. 17.) 
t Helmholtz tells us (Populare ivissenschaftliche 
Vortrdge, 3tes Heft, p. 64) that even in a stereo- 
scopic "arrangement the presence of a wrong cast 
shadow sufficed to disturb the illusion. 
* The perception of magnitude is closely con- 
nected with that of distance, and is similarly apt 
to take an illusory form. I need only refer to the 
well-known simple optical contrivances for increas- 
ing the apparent magnitude of objects. I ought, 
perhaps, to add that 1 do not profess to give a com- 
plete account of optical illusions here, but only to 
select a few prominent varieties, with a view to 
illustrate general principles of illusion. For a fuller 
account of the various mechanical arrangements for 
producing optical illusion, I must refer the reader to 
the writings of Sir D. Brewster and Helmholtz. \ PSYCHOLOGICAL STUDY. 
This effect is found to be the more striking 
in proportion to the familiarity of the form. 
The value of these means of producing illu- 
sion at the command of the painter, may be 
illustrated by the following fact, which I 
borrow from Helmholtz. If you place two 
pieces of cardboard which correspond to 
portions of one form at the sides and in 
The following drawing of a long box-shaped 
solid at once seems to stand out to the eye. 
This habitual interpretation of the flat in 
art as answering to objects in relief, or having 
depth, can only be understood when it is re- 
membered that our daily experience gives us 
myriads of instances in which the effect of 
such flat representations answers to solid 
receding forms. That is to say, in the case 
of all distant objects, in the perception of 
which the dissimilarity of the retinal pictures 
and the feeling of convergence take no part, 
we have to interpret solidity and relations of 
nearer and further by such signs as linear 
perspective and cast shadow. On the other 
hand, it is only in the artificial life of indoors, 
on our picture-covered walls, that we expe- 
rience such effects without discovering cor- 
responding realities. Hence a deeply organ- 
ized habit of taking these impressions as 
answering to the solid and not to the flat. 
If our experience had been quite different; 
if, for example, we had been brought up in 
an empty room, amid painted walls, and had 
been excluded from the sight of the world of 
receding objects outside, we might easily 
have formed an exactly opposite habit of 
taking the actual mountains, trees, etc., of 
the distant scene to be pictures laid on a flat 
surface. 
It follows from this that, with respect to 
the distant parts of a scene, pictorial art 
possesses the means of perfect imitation; 
and here we see that a complete illusory 
effect is obtainable. I need but to refer to 
the well-known devices of linear and aerial 
perspective, by which this result is secured.* 
front of a third piece, in the way represented 
above, so as just to allow the eye to follow 
the contour of this last, and then look at this 
arrangement from a point at some little dis- 
! tance with one eye, you easily suppose that 
j it stands in front of the side pieces. The 
explanation of the illusion is that this partic- 
ular arrangement powerfully suggests that 
the outline of the whole figure, of which the 
two side pieces are parts, is broken by an 
intervening object. Owing to the force of 
these and other suggestions, it is easy for the 
spectator, when attending to the background 
of a landscape painting, to give himself up 
for a moment to the pleasant delusion that 
he is looking at an actual receding scene. 
In connection with pictorial delusion, I 
may refer to the well-known fact, that the 
eye in a portrait seems to follow the specta- 
tor, or that a gun, with its muzzle pointing 
straight outwards, appears to turn as the 
spectator moves.* These tricks of art have 
puzzled many people, yet their effect is easily 
understood, and has been very clearly ex- 
plained by Sir D. Brewster, in the work 
already referred to (letter v.). They depend 
on the fact that a painting, being a flat pro- 
jection only and not a solid, continues to 
present the front view of an object which it 
represents wherever the spectator happens 
to stand. Were the eye in the portrait a 
real eye, a side movement of the spectator 
would, it is evident, cause him to see less of 
the pupil and more of the side of the eyeball, 
* Among the means of giving a vivid sense of 
depth to a picture, emphasized" by Helmholtz, is 
diminishing magnitude. It is obvious that the 
perceptions of real magnitude and distance are 
mutually involved. When, for example, a picture 
represents a receding series of objects, as animals, 
trees, or buildings, the sense of the third dimen- 
sion is rendered much more clear. 
* A striking example of this was given in a paint- 
ing- by Andsell, of a sportsman in the act of shoot- 
ing, exhibited in the Roval Academy in 1870. 24 
ILLUSIONS: 
and he would only continue to see the full pu- 
pil when the eye followed him. We regard 
the eye in the picture as a real eye having re- 
lief, and judge accordingly. 
We may fall into similar illusions respect- 
ing distance in auditory perception. A 
change of wind, an unusual stillness in the 
air, is quite sufficient to produce the sense 
that sounding objects are nearer than they 
actually are. The art of the ventriloquist 
manifestly aims at producing this kind of 
illusion. By imitating the dull effect of a 
distant voice, he is able to excite in the 
minds of his audience a powerful conviction 
that the sounds proceed from a distant point. 
There is little doubt that ventriloquism has i 
played a conspicuous part in the arts of divi- 
nation and magic. 
Misconception of Local Arrangeme7it.—Let 
us now pass to a class of illusions closely 
related to those having to do with distance, 
but involving some special kind of circum- 
stance which powerfully suggests a particu- 
lar arrangement in space. One of the most 
striking examples of these is the erroneous 
localization of a quality in space, that is to 
say, the reference of it to an object nearer or 
further off than the right one. Thus, when 
we look through a piece of yellow glass at a 
dull, wintry landscape, we are disposed to 
imagine that we are looking at a sunny scene 
of preternatural warmth. A moment’s re- 
flection would tell us that the yellow tint 
with which the objects appear to be suffused, 
-comes from the presence of the glass; yet, in 
spite of this, the illusion persists with a 
curious force. The explanation is, of course, 
that the circumstances are exceptional, that 
in a vast majority of cases the impression of 
color belongs to the object and not to an in- 
tervening medium,* and that consequently 
we tend to ignore the glass, and to refer the 
color to the objects themselves. 
When, however, the fact of the existence of 
a colored medium is distinctly present to the 
mind, we easily learn to allow for this, and to 
recognize one colored surface correctly 
through a recognized medium. Thus, we 
appear to ourselves to see the reflected im- 
ages of the wall, etc., of a room, in a bright 
mahogany table, not suffused with a reddish 
yellow tint, as they actually are—and may be 
seen to be by the simple device of looking at 
a small bit of the image through a tube, but 
in their ordinary color. We may be said to 
fall'into illusion here in so far as we overlook 
the exact quality of the impression actually 
made on the eye. This point will be touched 
on presently. Here I am concerned to show 
that this habit of allowing for the colored 
medium may, in its turn, occasionally lead to 
plain and palpable illusion. 
The most striking example of this error is 
to be met with among the curious phenomena 
of color-contrast already referred to. In 
many of these cases the appearance of the 
constrasting color is, as I have observed, due 
to a temporary modification of the nervous sub- 
stance. Yet it is found that this organic fac- 
tor does not wholly account for the phenom- 
ena. For example, Meyer made the follow- 
ing experiment. He covered a piece of green 
paper by a sheet of thin transparent white 
paper. The color of this double surface was, 
of course, a pale green. He then introduced 
a scrap of gray paper between the two sheets, 
and found that, instead of looking whitish as 
it really was, it looked rose-red. Whatever 
the color of the under sheet the gray scrap 
took the complementary hue. If, however, 
the piece of gray paper is put outside the thin 
sheet, it looks gray; and what is most re- 
markable is that when a second piece is put 
outside, the scrap inside no longer wears the 
complementary hue. 
There is here evidently something more 
than a change of organic conditions ; there is 
an action of experience and suggestion. The 
reason of our seeing the scrap rose-red in one 
case and neutral gray in another, is that in 
the first instance we vividly represent to our- 
selves that we are looking at it through a 
greenish veil (which is, of course, a part of 
the illusion); for rose-red seen through a 
greenish medium would, as a matter of fact, 
be light gray, as this scrap is. Even if we al- 
low that there always exists after an impres- 
sion of color a temporary organic disposition 
to see the complementary hue, this does not 
suffice as an explanation of these cases; we 
have to conclude further that imagination, 
led by the usual run of our experience, is 
here a co-operant factor, and helps to deter- 
mine whether the complementary tint shall 
be seen or not. 
Misinterpretation of Form.—More complex 
and circumscribed associations take part in 
those errors which we occasionally commit 
respecting the particular form of objects. 
This has already been touched on in dealing 
with artistic illusion. The disposition of the 
eye to attribute solidity to a flat drawing is 
the more powerful in proportion to the famil- 
iarity of the form. Thus, an outline drawing 
of a building is apt to stand out with special 
force. 
Another curious illustration of this is the 
phenomenon known as the conversion of the 
concave mold or matrix of a medal into the 
corresponding convex relief. If, says Helm- 
holtz, the mold of a medal be illuminated 
by a light falling obliquely so as to produce 
strong shadows, and if we regard this with 
one eye, we easily fall into the illusion that it 
is the original raised design, illuminated from 
the opposite side. As a matter of fact, the visual 
impression produced by a concave form with 
the light falling on one side, very closely re- 
sembles that produced by a corresponding 
convex form with the light falling on the 
other side. At the same time, it is found 
that the opposite mode of conversion, that is 
to say, the transformation of the raised into 
the depressed form, though occurring occa- 
sionally, is much less frequent. Now, it may 
be asked, why should we tend to transform the 
* This is at least true of all near objects. A PSYCHOLOGICAL STUDY. 
25 
concave into the convex, rather than the con- 
vex into the concave ? The reader may easily 
anticipate the answer from what has been said 
about the deeply fixed tendency of the eye to 
solidify a plane surface. We are rendered 
much more familiar, both by nature and bv art, 
with raised (cameo) design than with depressed 
design (intaglio), and we instinctively inter- 
pret the less familiar form by the more famil- 
iar. This explanation appears to be borne out 
by the fact emphasized by Schroeder that the 
illusion is mtfth more powerful if the design 
is that of some well-known object, as the 
human head or figure, or an animal form, 
•or leaves.* 
Another illustration of this kind of illusion 
recently occurred in my own experience. 
Nearly opposite to my window came a narrow 
space between two detached houses. This 
was, of course, darker than the front of the 
houses, and the receding parallel lines of the 
bricks appeared to cross this narrow vertical 
shaft obliquely. I could never look at this 
without seeing it as a convex column, round 
which the parallel lines wound obliquely. 
Others saw it as I did, though not always 
with the same overpowering effect. I can 
only account for this illusion by help of the 
general tendency of the eye to solidify im- 
pressions drawn from the flat, together with 
the effect of special types of experience, more 
particularly the perception of cylindrical forms 
in trees, columns, etc. 
It may be added that a somewhat similar 
illustration of the action of special types of 
experience on the perception of individual 
form may be found in the region of hearing. 
The powerful disposition to take the finely 
graduated cadences of sound produced by 
the wind for the utterances of a human voice, 
is due to the fact that this particular form 
and arrangement of sound has deeply im- 
pressed itself on our minds in connection 
with numberless utterances of human feeling. 
Illusions of Recognition.—As a last illustra- 
tion of comparatively passive illusions, 1 may 
refer to the errors which we occasionally 
•commit in recognizing objects. As I have 
already observed, the process of full and clear 
recognition, specific and individual, involves 
a classing of a number of distinct aspects of 
the object, such as color, form, etc. Accord- 
ingly, when in a perfectly calm state of mind 
we fall into illusion wfith respect to any ob- 
ject plainly visible, it must be through some 
accidental resemblance between the object 
and the other object or class of objects with 
which we identify it. In the case of individ- j 
ual identification such illusions are, of course, I 
comparatively rare, since here there are in- 
volved so many characteristic differences. j 
On the other hand, in the case of specific 
recognition there is ample room for error, 
especially in those kinds of more subtle rec- 
ognition to which I have already referred. 
To “ recognize ” a person as a Frenchman or 
a military man, for example, is often an er- 
roneous process. Logicians have included 
this kind of error under what they call “fal- 
lacies of observation.” 
Errors of recognition, both specific and in- 
dividual, are, of course, more easy in the case 
of distant objects or objects otherwise indis- 
tinctly seen. It is noticeable in these cases 
that, even when perfectly cool and free from 
emotional excitement, we tend to interpret 
such indistinct impressions according to cer- 
tain favorite types of experience, as the hu- 
man face and figure. Our interpretative 
imagination easily sees traces of the human 
form in cloud, rock, or tree-stump. 
Again, even when there is no error of rec- 
ognition, in the sense of confusing one object 
with other objects, there may be partial illu- 
sion. I have remarked that the process of 
recognizing an object commonly involves an 
overlooking of points of diversity in the ob- 
ject, or aspect of the object, now present. And 
sometimes this inattention to what is actually 
present includes an error as to the actual 
visual sensation of the moment. Thus, for 
example, when I look at a sheet of w hite 
paper in a feebly lit room, I seem to see its 
| whiteness. If, however, I bring it near the 
| window, and let the sun fall on a part of it, 
I at once recognize that what I have been 
seeing is not white, but a decided gray. 
Similarly, when 1 look at a brick viaduct a 
mile or two off, I appear to myself to recognize 
its redness. In fact, however, the impression 
of color which I receive from the object is not 
that of brick-red at all, but a much less de- 
cided tint; which I may easily prove by bend- 
ing my head downwards and letting the scene 
image itself on the retina in an unusual way, 
in which case the recognition of the object 
as a viaduct being less distinct, I am better 
able to attend to the exact shade of the color. 
Nowhere is this inattention to the sensa- 
tion of the moment exhibited in so striking a 
manner as in pictorial art. A picture of 
Meissonier may give the eye a representation 
of a scene in which the objects, as the human 
figures and horses, have a distinctness that 
belongs to near objects, but an apparent 
magnitude that belongs to distant objects. 
So again, it is found that the degree of lumi- 
nosity or brightness of a pictorial representa- 
tion differs in general enormously from that 
of the actual objects. Thus, according to the 
calculations of Helmholtz,* a picture repre- 
senting a Bedouin’s white raiment in blinding 
sunshine, will, when seen in a fairly lit gallery, 
have a degree of luminosity reaching only to 
about one-thirtieth of that of the actual ob- 
ject. On the other hand, a painting repre- 
senting marble ruins illuminated by moon- 
light, will, under the same conditions of illu- 
mination, have a luminosity amounting to as 
* Helmholtz remarks (of>. cit., p. 628) that the dif- 
ficulty of seeing the concave cast as convex is prob- 
ably due to the presence of the cast shadow. This 
has, no doubt, some effect: yet the consideration 
urged in the text appears to me to be the most im- 
portant one. 
* Popnldre missenschaftlichc Vortr&ge, 3tes Heft, 
pp. 71, 72. ILLUSIONS : 
much as from ten to twenty thousand times 
that of the object. Yet the spectator does 
not notice these stupendous discrepancies. 
The representation, in spite of its vast dif- 
ference, at once carries the mind on to the 
actuality, and the spectator may even appear 
to himself, in moments of complete absorp- 
tion, to be looking at the actual scene. 
The truly startling part of these illusions 
is, that the'direct result of sensory stimula- 
tion appears to be actually displaced by a 
mental image. Thus, in the case of Meyer’s 
experiment, of looking at the distant viaduct, 
and of recognizing an artistic representation, 
imagination seems in a measure to take the 
place of sensation, or to blind the mind to 
what is actually before it. 
The mystery of the process, however, 
greatly disappears when it is remembered 
that what we call a conscious “ sensation ” is 
really compounded of a result of sensory 
stimulation and a result of central reaction, 
of a purely passive impression and the mental 
activity involved in attending to this and 
classing it.* This being so, a sensation may 
be modified by anything exceptional in the 
mode of central reaction of the moment. 
Now, in all the cases just considered, we have 
one common feature, a powerful suggestion of 
the presence of a particular object or local 
arrangement. This suggestion, taking the 
form of a vivid mental image, dominates and 
overpowers the passive impression. Thus, in 
Meyer’s experiment, the mind is possessed 
by the supposition that we are looking at the 
gray spot through a greenish medium. So 
in the case of the distant viaduct, we are 
under the mastery of the idea that what we 
see in the distance is a red brick structure. 
Once more, in the instance of looking at the 
picture, the spectator’s imagination is en- 
chained by the vivid representation of the 
object for which the picture stands, as the 
marble ruins in the moonlight or the Bedouin 
in the desert. 
It may be well to add that this mental un- 
certainty as to the exact nature of a present 
impression is necessitated by the very condi- 
tions of accurate perception. If, as I have 
said, all recognition takes place by overlook- 
ing points of diversity, the mind must, in 
course of time, acquire a habit of not attend- 
ing to the exact quality of sense-impressions 
in all cases where the interpretation seems 
plain and obvious. Or, to use Helmholtz’s 
words, our sensations are, in a general way, 
of interest to us only as signs of things, and 
if we are sure of the thing, we readily over- 
look the precise nature of the impression. 
In short, we get into the way of attending 
only to what is essential, constant, and char- 
acteristic in objects, and disregarding what is 
variable and accidental.t Thus, we attend, 
in the first place, to the form of objects, the 
most constant and characteristic element of 
all, being comparatively inattentive to color, 
which varies with distance, atmospheric 
changes, and mode of illumination. So we 
attend to the relative magnitude of objects 
rather than to the absolute, and to the rela- 
tive intensities of light and shade rather than 
to the absolute; for in so doing we are not- 
ing what is constant for all distances and 
modes of illumination, and overlooking what 
is variable. And the success of pictorial art 
depends on the observance of mis law of per- 
ception. . 
These remarks at once point out the limits 
of these illusions. In normal circumstances, 
an act of imagination, however vivid, cannot 
create the semblance of a sensation which 
is altogether absent; it can only slightly 
modify the actual impression by interfering 
with that process of comparison and classi- 
fication which enters into all definite deter- 
mination of sensational quality. 
Another great fact that has come to light 
in the investigation of these illusions is that 
oft-recurring and familiar types of experience 
leave permanent dispositions in the mind. 
As I said when describing the process of per- 
ception, what has been frequently perceived 
is perceived more and more readily. It fol- 
lows from this that the mind will be habit- 
ually disposed to form the corresponding 
mental images, and to interpret impressions- 
by help of these. The range of artistic sug- 
gestion depends on this. A clever draughts- 
man can indicate a face by a few rough 
touches, and this is due to the fact that the 
spectator’s mind is so familiarized, through 
recurring experience and special interest, 
with the object, that it is ready to construct 
the requisite mental image at the slightest 
external suggestion. And hence the risk of 
hasty and illusory interpretation. 
These observations naturally conduct us 
to the consideration of the second great 
group of sense-illusions, which I have marked 
off as active illusions, where the action of a 
pre-existing intellectual disposition becomes 
much more clearly marked, and assumes the 
form of a free imaginative transformation 
of reality. 
CHAPTER VI. 
ILLUSIONS OF PERCEPTION—continued. 
B. Active Illusions.—When giving an ac- 
count of the mechanism of perception, 7 
spoke of an independent action of the im- 
agination which tends to anticipate the proc- 
ess of suggestion from without. Thus, when 
expecting a particular friend, I recognize his 
* See, on this point, some excellent remarks by 
G H. Lewes, Problems of Life and Mindthird 
series, vol. ii. p. 275. 
+ To some extent this applies terthe changes of 
apparent magnitude due to altered position. Thus, 
we do not attend to the reduction of the height of 
a small object which we are wont to handle, when 
it is placed far below the level of the eye. And 
hence the error people make in judging of the 
point in the wall or skirting which a hat wil reach 
when placed on the ground. V PSYCHOLOGICAL STUDY. 
form much more readily than when my mind 
has not been preoccupied with his image. 
A little consideration will show that this 
process must be highly favorable to illusion, 
lo begin with, even if the preperception be 
correct, that is to say, if it answer to the per- 
ception, the mere fact of vivid expectation 
will affect the exact moment of the completed 
act of perception. And recent experiment 
shows that in certain cases such a previous 
activity of expectant attention may even lead 
to the illusory belief that the perception takes 
place before it actually does.* 
A more palpable source of error resides in 
the risk of the formation of an inappropriate 
preperception. If a wrong mental image 
happens to have been formed and vividly 
entertained, and if the actual impression fits 
in to a certain extent with this independently 
formed preperception, we may have a fusion 
of the two which exactly simulates the form 
of a complete percept. Thus, for example, 
in the case just supposed, if another person, 
bearing some resemblance to our expected 
friend, chances to come into view, we may 
probably stumble into the error of taking one 
person for another. 
On the physical side, we may, agreeably to 
the hypothesis mentioned above, express this 
result by saying that, owing to a partial iden- 
tity in the nervous processes involved in the 
anticipatory image and the impression, the 
two tend to run one into the other, constitut- 
ing one continuous process. 
There are different ways in which this inde- 
pendent activity of the imagination may fal- 
sify our perceptions. Thus, we may volunta- 
rily choose to entertain a certain image for a 
moment, and to look at the impression in a 
particular way, and within certain limits such 
capricious selection of an interpretation is 
effectual in giving a special significance to an 
impression. Or the process of independent 
preperception may go on apart from our voli- 
tions, and perhaps in spite of these, in which, 
case the illusion has something of the irresist- 
ible necessity of a passive illusion. Let us 
consider separatety each mode of production. 
Voluntary Selection of Interpretation.—The 
action of a capricious exercise of the imagi- 
nation in relation to an impression is illus- 
trated in those cases where experience and 
suggestion offer to the interpreting mind an 
uncertain sound, that is to say, where the 
present sense-signs are ambiguous. Here we 
obviously have a choice of interpretation. 
And it is found that, in these cases, what we 
see depends very much on what we wish to 
see. The interpretation adopted is still, in a 
sense, the result of suggestion, but of one 
particular suggestion which the fancy of the 
moment determines. Or, to put it another 
way, the caprice of the moment causes the 
attention to focus itself in a particular man- 
ner, to direct itself specially to certain aspects 
and relations of objects. 
The eye’s interpretation of movement, 
already referred to, obviously offers a wide 
field for this play of selective imagination. 
When looking out of the window of a rail- 
way carriage, I can at will picture to my 
mind the trees and telegraph posts as mov- 
ing objects. Sometimes the true interpreta- 
tion is so uncertain that the least inclination 
to view the phenomenon in one way deter- 
mines the result. This is illustrated in a 
curious observation of Sinsteden. One even- 
ning, or. approaching a windmill obliquely 
from one side, which under these circum- 
stances he saw only as a dark silhouette 
against a bright sky, he noticed that the sails 
appeared to go, now in one direction, now 
in another, according as he imagined himself 
looking at the front or at the back of the 
windmill.* 
In the interpretation of geometrical draw- 
ings, as those of crystals, there is, as I have 
observed, a general tendency to view the flat 
delineation as answering to a raised object, 
or a body in relief, according to the common 
run of our experience. Yet there are cases 
where experience is less decided, and where, 
consequently, we may regard any particular 
line as advancing or receding. And it is 
found that when we vividly imagine that the 
drawing is that of a convex or concave sur- 
face, we see it to be so, with all the force of 
a complete perception. The least disposition 
to see it in the other way will suffice to re- 
verse the interpretation. Thus, in the follow- 
ing drawing, the reader can easily see at will 
Fig. 5. 
something answering to a truncated pyramid, 
or to the interior of a cooking vessel. 
Similarly, in the accompanying figure of a 
transparent solid, I can at will select either 
of the two surfaces which approximately 
face the eye and regard it as the nearer, the 
other appearing as the hinder surface looked 
at through the body. 
Again, in the next drawing, taken from 
Schroeder, one may, by an effort of will, see 
the diagonal step-like pattern, either as the 
* I refer to the experiments made by Exner, 
Wundt, and others, in determining the time elaps- 
ing between the giving of a signal to a person and 
the execution of a movement in response. “ It is 
found,” says Wundt, “ by these experiments that 
the exact moment at which a sense-impression is 
perceived depends on the amount of preparatory 
self-accommodation of attention. ” (See Wundt, 
Physiologische Psychologies ch. xix., especially p. 
Ti$,et seq.) 
Quoted by Helmholtz, op. oil., p. 626.. ILLUSIONS: 
view from above of the edge of an advancing 
piece of wall at a, or as the view from below 
of the edge of an advancing (overhanging) 
piece of wall at A 
tion offers itself in looking at elaborate dec- 
orative patterns. When we strongly imagine 
any number of details to be elements of one 
figure, they seem to become so; and a given 
detail positively appears to alter in character 
according as it is viewed as an element of a 
more or less complex figure. 
These examples show what force belongs 
to a vivid preconception, if this happens to 
fit only very roughly the impression of the 
moment, that is to say, if the interpretative 
image is one of the possible suggestions of 
the impression. The play of imagination 
takes a wider range in those cases where the 
impression is very indefinite in character, 
easily allowing of a considerable variety of 
imaginative interpretation. 
I referred at the beginning of this account 
of sense-illusions to the readiness with which 
the mind deceives itself with respect to the 
nature and causes of the vague sensations 
which usually form the dim background of 
our mental life. A person of lively imagina- 
tion, by trying to view these in a particular 
way, and by selectively attending to those 
aspects of the sensation which answer to the 
caprice of the moment, may give a variety 
of interpretations to one and the same set of 
sensations. For example, it is very easy to 
get confused with respect to those tactual 
and motor feelings which inform us of the 
position of our bodily members. And so, 
when lying in bed, and attending to the sen- 
sations connected with the legs, we may easily 
delude ourselves into supposing that these 
members are arranged in a most eccentric 
fashion. Similarly, by giving special heed to 
the sensations arising in connection with the 
condition of the skin at any part, we may 
amuse ourselves with the strangest fancies as 
to what is going on in these regions. 
Again, when any object of visual percep- 
tion is indistinct or indefinite in form, there 
is plainly an opening for this capricious play 
of fancy in transforming the actual. This is 
illustrated in the well-known pastime of dis- 
covering familiar forms, such as those of the 
human head and animals, in distant rocks 
and clouds, and of seeing pictures in the fire, 
and so on. The indistinct and indefinite 
shapes of the masses of rock, cloud, or glow- 
ing coal, offer an excellent field for creative 
fancy, and a person of lively imagination will 
discover endless forms in what, to an unim- 
aginative eye, is a formless waste. Johannes 
Muller relates that, when a child, he used to 
spend hours in discovering the outlines of 
forms in the partly blackened and cracked 
stucco of the house that stood opposite to 
his own.* Here it is plain that, while expe- 
rience and association are not wholly absent, 
but place certain wide limits on this process 
of castle-building, the spontaneous activity 
of the percipient mind is the great determin- 
ing force. 
So much as to the influence of a perfectly 
Fig. 6. 
These last drawings are not in true per- 
spective on either of the suppositions adopted, 
wherefore the choice is easier. But even 
when an outline form is in perspective, a 
strenuous effort of imagination may suffice to 
Fig. 7. 
bring about a conversion of the appearance. 
Thus, if the reader will look at the drawing 
of the box-like solid (Fig. 3, p. 23), he will 
find that, after a trial or two, he succeeds in 
seeing it as a concave figure representing the 
cover and two sides of a box as looked at 
from within.* 
Many of my readers, probably, share in 
my power of variously interpreting the rela- 
tive position of bands or stripes on fabrics 
such as wall-papers, according to wish. I find 
that it is possible to view now this stripe or set 
of stripes as standing out in relief upon the 
others as a ground, now these others as 
advancing out of the first as a background. 
The difficulty of selecting either interpreta- 
tion at will becomes greater, of course, in 
those cases where there is a powerful sugges- 
tion of some particular local arrangement, 
as, for example, the case of patterns much 
brighter than the ground, and especially of 
such as represent known objects, as flowers. 
Yet even here a strong effort of imagination 
will often suffice to bring about a conversion 
of the first appearance. 
A somewhat similar choice of interpreta- 
* When the drawing, by its adherence to the 
laws of perspective, does not powerfully determine 
the eye to see it in one way rather than in the other 
(as in Figs. 5 to 7), the disposition to see the one 
form rather than the other points to differences in 
the frequency of the original forms in our daily 
experience. At the same time, it is to be observed 
that, after looking at the drawing for a time under 
each aspect, the suggestion now of the one and 
now of the other forces itself on the mind in a 
curious and unaccountable way. 
* Ueber die fihantastischen GesicJttserscheiftu 
gen, p. 45. A PS VCHOLOGICAL STUDY. 
tmfettered voluntary attention on the deter- 
mination of the stage of preperception, and, 
through this, of the resulting interpretation. 
Let us now pass to cases in which this direc- 
tion of preperception follows not the caprice 
of the moment, but the leading of some fixed 
predisposition in the interpreter’s mind. In 
these cases attention is no longer free, but 
fettered, only it is now fettered rather from 
within than from without; that is to say, the 
dominating preperception is much more the 
result of an independent bent of the imagina- 
tion than of some suggestion forced on the 
mind by the actual impression of the moment. 
Involuntary Mental Preadjustmen'.—If we 
glance back at the examples of capricious se- 
lection just noticed, we shall see that they are 
really limited not only by the character of the 
impression of the time, but also by the men- 
tal habits of the spectator. That is to say, we 
find that his fancy runs in certain definite di- 
rections, and takes certain habitual forms. It 
has already been observed that the percipient 
mind has very different attitudes with respect 
to various kinds of impression. Toward 
some it holds itself at a distance, while 
toward others, it at once bears itself famil- 
iarly; the former are such as answer to its 
previous habit and bent of imagination, the 
latter such as do not so answer. 
This bent of the interpretative imagination, 
assumes, as we have already seen, two forms, 
that of a comparatively permanent disposi- 
tion, and that of a temporary state of expec- 
tation or mental preparedness. Illusion may 
arise in connection with either of these forms. 
Let us illustrate both varieties, beginning 
with those which are due to a lasting mental 
disposition. 
It is impossible here to specify all the 
causes of illusion residing in organized tend- 
encies of the mind. The whole past men- 
tal life, with its particular shade of experi- 
ence, its ruling emotions, and its habitual di- 
rection of fancy, serves to give a particular 
color to new impressions, and so to favor il- 
lusion. There is a “ personal equation ” in 
perception as in belief—an amount of errone- 
ous deviation from the common average view 
of external things, which is the outcome of 
individual temperament and habits of mind. 
Thus, a naturally timid man will be in gen- 
eral disposed to see ugly and fearful objects 
where a perfectly unbiased mind perceives 
nothing of the kind; and the forms which 
these objects of dread will assume are deter- 
mined by the character of his past experience, 
and by the customary direction of his imag- 
ination. 
In perfectly healthy states of mind this in- 
fluence of temperament and mental habit on 
the perception of external objects is, of course, 
very limited ; it shows itself more distinctly, 
as we shall see, in modifying the estimate of 
things in relation to the aesthetic and other 
feelings. This applies to the mythical poeti- 
cal way of looking at Mture-—a part of our 
subiect to which we shall have to return later 
on 
Passing now from the effect of such perma- 
nent dispositions, let us look at the more 
striking results of temporary expectancy of 
mind. 
When touching on the influence of such a 
temporary mental attitude in the process of 
correct perception, I remarked that this readi- 
ness of mind might assume an indefinite or a 
definite form \Ve will examine the effect of 
each kind in the production of illusion. 
Action of Sub-Expectation.—First of all, 
then, our minds may at the particular moment 
be disposed to entertain any one of a vaguely 
circumscribed group of images. Thus, to re- 
turn to the example already referred to, when 
in Italy, we are in a state of readiness to 
frame any of the images that we have learnt 
to associate with this country. We may not 
be distinctly anticipating any one kind of ob- 
ject, but are nevertheless in a condition of 
sub-expectation with reference to a large num- 
ber of objects. Accordingly, when an im- 
pression occurs which answers only very 
roughly to one of the associated images, there 
is a tendency to superimpose the image on 
the impression. In this way illusion arises. 
Thus, a man, when strolling in a cathedral, 
will be apt to take any kind of faint hollow 
sound for the soft tones of an organ. 
The disposition to anticipate fact and 
reality in this way will be all the stronger if, 
as usually happens, the mental images thus 
lying ready for use have an emotional color- 
ing. Emotion is the great disturber of all 
intellectual operations. It effects marvel- 
ous things, as we shall presently see, in the 
region of illusory belief, and its influence is 
very marked in the seemingly cooler region 
of external perception. The effect of any 
emotional excitement appears to be to give 
a preternatural vividness and persistence to 
the ideas answering to it, that is to say, the 
ideas which are its excitants, or which are 
otherwise associated with it. Owing to this 
circumstance, when the mind is under the 
temporary sway of any feeling, as, for ex- 
ample, fear, there will be a special readiness, 
to interpret objects by help of images con- 
gruent with the emotion. Thus, a man under 
the control of fear will be ready to see any 
kind of fear-inspiring object whenever there 
is any resemblance to such in the things 
actually present, to his vision. The state of 
awe which the surrounding circumstances of 
a spiritualist stance inspires produces a gen- 
eral readiness of mind to perceive what is 
strange, mysterious, and apparently miracu- 
lous. 
It is worth noting, perhaps, that those de- 
lightful half-illusions which imitative art 
seeks to produce are greatly favored by such 
a temporary attitude of the interpreting im- 
agination In the theater, for example, we 
are prepared for realizing the semblance of 
life that is to be unfolded before us. We 
come knowing that what is to be performed 
aims at representing a real action or actual 
series of events. We not improbably work 
ourselves into a slightly excited state in an- 30 
ILLUSIONS: 
ticipation of such a representation. More 
than this, as the play progresses, the reali- 
zation of what has gone before produces a 
strong disposition to believe in the reality 
of what is to follow. And this effect is pro- 
portionate to the degree of coherence and 
continuity in the action. In this way, there 
is a cumulative effect on the m ud. If the 
action is good, the illusion, as every play- 
goer knows, is most complete toward the 
end. 
Were it not for all this mental preparation, 
the illusory character of the performance 
would be too patent to view, and our enjoy- 
finent would suffer. A man is often aware 
of this when coming into a theater during 
the progress of a piece before his mind ac- 
commodates itself to the meaning of the 
play. And the same thing is recognizable 
in the fact that the frequenter of the theater 
has his susceptibility to histrionic delusion 
increased by acquiring a habit of looking 
out for the meaning of the performance. 
Persons who first see a play, unless they be 
of exceptional imagination and have thought 
much about the theater—a? Charlotte Bronte, 
for instance—hardly feel the illusion at all. 
At least, this is true of the opera, where the 
■departure from reality is so striking that the 
impression can hardly fail to be a ludicrous 
one, till the habit of taking the performance 
for what it is intended to be is fully formed.* 
A similar effect of intellectual preadjust- 
ment is observable in the fainter degrees of 
illusion produced by pictorial art. Here the 
undeceiving circumstances, the flat surface, 
the surroundings, and so on, would sometimes 
be quite sufficient to prevent the least degree 
of illusion, were it not that the spectator 
comes prepared to see a representation of 
some real object. This is our state of mind 
when we enter a picture gallery or approach 
what we recognize as a picture on the wall of 
a room. A savage would not “realize” a 
slight sketch as soon as one accustomed to 
pictorial representation, and ready to perform 
the required interpretative act.j 
So much as to the effect of an indefinite 
state of sub-expectation in misleading our 
perceptions. Let us now glance at the re- 
sults of definite pre-imagination, including 
what are generally known as expectations. 
Effects of Vivid Expectation.—Such expec- 
tations may grow out of some present object- 
ive facts, which serve as signs of the expected 
event; or they may arise by way of verbal 
suggestion; or, finally, they "may be due to 
internal spontaneous imagination. 
In the first place, then, the expectations 
may grow out of previous perceptions, while, 
nevertheless, the direction of the expectation 
may be a wrong one. Here the interpreting 
imagination is, in a large sense, under the 
control of external suggestion, though, with 
respect to the particular impression that is 
misconstrued, it may be regarded as acting 
independently and spontaneously. 
Illustrations of this effect in producing illu- 
sion will easily occur to the reader. If I 
happen to have heard that a particular per- 
son has been a soldier or clergyman, I tend 
to see the marks of the class in this person, 
and sometimes find that this process of rec- 
ognition is altogether illusory. Again, let us 
suppose that a person is expecting a friend 
by a particular train. A passenger steps out 
of the train bearing a superficial resemblance 
to his friend; in consequence of which he 
falls into the error of false identification 
The delusions of the conjurer depend on 
a similar principle. The performer tells his 
audience that he is about to do a certain 
thing, for example, take a number of animals 
out of a small box which is incapable of 
holding them. The hearers, intent on what 
has been said, vividly represent to themselves 
the action described. And in this way their 
attention becomes bribed, so to speak, before 
hand, and fails to notice the inconspicuous 
movements, which would at once clear up the 
mystery. Similarly with respect to the illu- 
sions which overtake people at spiritualist 
seances. The intensity of the expectation of 
a particular kind of object excludes calm at- 
tention to what really happens, and the 
slightest impressions which answer to signs 
of the object anticipated are instantly seized 
by the mind and worked up into illusory per- 
ceptions. 
It is to be noted that even when the im- 
pression cannot be made to tally exactly with 
the expectation, the force of the latter often 
effects a grotesque confusion of the percep- 
tion. If, for example, a man goes into a 
familiar room in the dark in order to fetch 
something, and for a moment forgets the 
particular door by which he has entered, his 
definite expectation of finding things in a 
certain order may blend with the order of 
impressions experienced, producing for the 
moment a most comical illusion as to the 
actual state of things. 
When the degree of expectation is un 
usually great, it may suffice to produce some 
thing like the counterfeit of a real sensation. 
This happens when the present circumstan 
ces are powerfully suggestive of an imme- 
diate event. The effect is all the more 
powerful, moreover, in those cases where the 
object or event expected is interesting or 
exciting, since here the mental image gains 
in vividness through the emotional excite- 
ment attending it. Thus, if I am watching • 
* Another side of histrionic illusion, the reading 
of the imitated feelings into the actors’ minds, win 
be dealt with in a later chapter. 
t In a finished painting of any size this prepara- 
tion is hardly necessary. In these cases, in spite of 
the great deviations from truth in pictorial repre- 
sentation already touched on, the amount of essen- 
tial agreement is so large and so powerful in its 
effect that even an intelligent animal will experience 
an illusion. Mr. Romanes sends me an interesting 
account of a dog, that had never been accustomed 
to pictures, having been put into a state of great 
excitement by the introduction of a portrait into a 
room, on a level with his eye. It is not at all im- 
probable that the lower animals, even when sane, 
are frequently the subjects of slight illusion. That 
animals dream is a fact which is observed as long 
ago as the age of Lucretius A PSYCHOLOGICAL STUDY. 
train off and know from all the signs that it 
is just about to start, I easily delude myself 
into the conviction that it has begun to start, 
when it is really still* An intense degree 
of expectation may, in such cases, produce 
something indistinguishable from an actual 
sensation. This effect is seen in such com- 
mon experiences as that the sight of food 
makes the mouth of a hungry man water; 
that the appearance of a surgical instrument 
produces a nascent sensation of pain; and 
that a threatening movement, giving a vivid 
anticipation of tickling, begets a feeling 
which closely approximates to the result of 
actual tickling. 
One or two very striking instances of such 
imagined sensations are given .by Dr. Car- 
penter.f Here is one. An officer who 
superintended the exhuming of a coffin 
rendered necessary through a suspicion of 
crime, declared that he already experienced 
the odor of decomposition, though it was 
afterwards found that the coffin was empty. 
It is, of course, often difficult to say, in 
such cases as these, how far elements of 
actual sensation co-operate in the production 
of the illusions. Thus, in the case just men- 
tioned, the odor of the earth may have been 
the starting-point in the illusion. In many 
cases, however, an imaginative mind appears 
to be capable of transforming a vivid expec- 
tation into a nascent stage of sensation. 
Thus, a mother thinking of her sick child in 
an adjoining room, and keenly on the alert 
for its voice, will now and again fancy she 
really hears it when others hear nothing at all. 
Transition to Hallucination.—It is plain 
that in these cases illusion approaches to 
hallucination. Imagination, instead of wait- 
ing on sensation, usurps its place and imi- 
tates its appearance. Such a “ subjective ” 
sensation produced by a powerful expectation 
might, perhaps, by a stretch of language, be 
regarded as an illusion, in the narrow sense, 
in so far as it depends on the suggestive 
force of a complete set of external circum- 
stances ; on the other hand, it is clearly an 
hallucination in so far as it is the production 
of the semblance of an external impression 
without any external agency corresponding 
to this. 
In the class of illusory expectations just 
considered the immediately present environ- 
ment still plays a part, though a much less 
direct part than that observable in the first 
large group of illusions. We will now pass to 
a second mode of illusory expectation, where 
imagination is still more detached from the 
present surroundings. 
A common instance of this kind of expecta- 
tion is the so-called “ intuition,” or presenti- 
ment, that something is going to happen, 
which expectation has no basis in fact. It 
does not matter whether the expectation has 
arisen by way of another’s words or by way 
of personal inclinations. A strong wish for 
a thing will, in an exalted state of mind, be- 
get a vivid anticipation of it. This subject 
will be touched on again under the Illusions 
of Belief. Here I am concerned to point out 
that such presentiments are fertile sources of 
sense-illusion. The history of Church mira- 
cles, visions, and the like amply illustrates 
the effect of a vivid anticipation in falsifying 
the perceptions of external things. 
In persons of a lively imagination any 
recent occupation of the mind with a certain 
kind of mental image may suffice to beget 
something equivalent to a powerful mode of 
expectation. For example, we are told by 
Dr. Tuke that on one occasion a lady, whose 
imagination had been dwelling on the sub- 
ject of drinking-fountains, “ thought she saw 
in a road a newly erected fountain, and even 
distinguished an inscription upon it, namely, 
‘ If any man thirst, let him come unto Me, 
and drink.’ She afterward found that what 
she had actually seen was only a few scat- 
tered stones.” * In many cases there seems 
to be a temporary preternatural activity of 
the imagination in certain directions, of 
which no very obvious explanation is discov- 
erable. Thus, we sometimes find our minds 
dwelling on some absent friend, without be- 
ing able to give any reason for this mental 
preoccupation. And in this way arise strong 
temporary leanings to illusory perception. 
It may be said, indeed, that all unwonted 
activity of the imagination, however it arises, 
has as its immediate result a temporary mode 
of expectation, definite or indefinite, which 
easily confuses our perceptions of external 
things. 
In proportion as this pre-existing imagina- 
tive impulse becomes more powerful, the 
amount of actual impression necessary to 
transform the mental image into an illusory 
perception becomes less; and, what is more 
important, this transformation of the internal 
image involves a larger and larger displace- 
ment of the actual impression of the moment. 
A man whose mind is at the time strongly 
possessed by one kind of image, will tend to 
project this outward with hardly any regard 
to the actual external circumstances. 
This state of things is most completely 
illustrated in many of the grosser illusions of 
the insane. Thus, when a patient takes any 
small objects, as pebbles, for gold and silver, 
under the influence of the dominant idea of 
being a millionaire, it is obvious that external 
* This kind of illusion is probably facilitated by 
the fact that the eye is often performing slight 
movements without any clear consciousness of 
them. See what was said about the limits of sen- 
sibility, p. 15. 
+ Mental Physiology, fourth edit., p. 158. 
J In persons of very lively imagination the mere 
representation of an object or event may suffice to 
bring about such a semblance of sensation. Thus, 
M. Taine (op. cit., vol. i. p. 94) vouches for the 
assertion that “ one of the most exact and lucid of 
modern novelists,” when working out in his 
imagination the poisoning of one of his fictitious 
characters, had so vivid a gustatory sensation of 
arsenic that he was attacked by a violent fit of in- 
digestion. 
* Mentioned by Dr. Carpenter (Mental Physiol- 
ogy, p. 207), where other curious examples are to be 
found. ILLUSIONS: 
suggestion has very little to do with the self-de- 
ception. The confusions into which the pa- 
tient often falls with respect to the persons 
before him show the same state of mind; for 
in many cases there is no discoverable indi- 
vidual resemblance between the person actu- 
ally present and the person for whom he is 
taken. 
It is evident that when illusion reaches 
this stage, it is scarcely distinguishable from 
what is specially known as hallucination. As 
I have remarked in setting out, illusion and 
hallucination shade one into the other much 
too gradually for us to draw any sharp line 
of demarkation between them. And here we 
see that hallucination differs from illusion 
only in the proportion in which the causes 
are present. When the internal imaginative 
impulse reaches a certain strength, it becomes 
self-sufficient, or independent of any external 
impression. 
This intimate relation between the extreme 
form of active illusion and hallucination may 
be seen, too, by examining the physical con- 
ditions of each. As I have already remarked, 
active illusion has for its physiological basis 
a state of sub-excitation, or an exceptional 
condition of irritability in the structures en- 
gaged in the act of interpretative imagination. 
The greater the degree of this irritability, the 
less will be the force of external stimulation 
needed to produce the effect of excitation, 
and the more energetic will be the degree of 
this excitation. Moreover, it is plain that 
this increase in the strength of the excitation 
will involve an extension of the area of exci- 
tation till, by and by, the peripheral regions 
of the nervous system may be involved just 
as in the case of external stimulation. This 
accounts for the gradual displacement of the 
impression of the moment by the mental 
image. It follows that when the irritability 
reaches a certain degree, the amount of ex- 
ternal stimulus needed may become a vanish- 
ing quantity, or the state of sub-excitation 
may of itself develop into one of full activity. 
Hallucinations.—I do not propose to go 
very fully into the description and explanation 
of hallucinations here, since they fall to a 
large extent under the category of distinctly 
pathological phenomena. Yet our study of 
illusions would not be complete without a 
glance abthis part of the subject. 
Hallucination, by which I mean the projec- 
tion of a mental image outward when there 
is no external agency answering to it, assumes 
one of two fairly distinct forms; it may pre- 
sent itself either as a semblance of an exter- 
nal impression with the minimum amount of 
interpretation, or as a counterfeit of a com- 
pletely developed percept. Thus, a visual 
hallucination may assume the aspect of a sen- 
sation of light or color which we vaguely re- 
fer to a certain region of the external world, 
or of a vision of some recognizable object. 
All of us frequently have incomplete visual 
and auditory hallucinations of the first order, 
whereas the complete hallucinations of the 
second order are comparatively rare. The 
first I shall call rudimentary, the second de- 
veloped, hallucinations. 
Rudimentary hallucinations may have 
either a peripheral or a central origin. They 
may first of all have their starting-point in 
those subjective sensations which, as we have 
seen, are connected with certain processes 
set up in the peripheral regions of the nerv- 
ous system. Or, secondly, they may origi- 
nate in a certain preternatural activity of the 
sensory centers, or “ sensorium,” in what has 
been called by German physiologists an au- 
tomatic excitation of the central structures, 
which activity may probably diffuse itself 
downward to the peripheral regions of the 
nerves. Baillarger would call hallucinations 
of the formed class “ psycho-sensorial,” those 
of the latter class purely “ psychical,” hallu- 
cinations.* 
It is often a matter of great difficulty to de- 
termine which part of the nervous system is 
originally concerned in these rudimentary 
hallucinations. It is probable that in normal 
life they are most frequently due to periph- 
eral disturbance. And it seems reasona- 
ble to suppose that where the hallucination 
remains in this initial stage of a very incom- 
pletely interpreted visual or auditory impres- 
sion, whether in normal or abnormal life, its 
real physiological source is the periphery. 
For the automatic excitation of the centers 
would pretty certainly issue in the semblance 
of some definite, familiar variety of sense-im- 
pression which, moreover, as a part of a com- 
plex state known as a percept, would in- 
stantly present itself as a completely formed 
quasi-percept. In truth, we may pretty safely 
argue that if it is the center which is directly 
thrown into a state of activity, it will be thrown 
into the usual complex, that is to say, percept 
tional, mode of activity. 
Let us now turn to hallucinations properly 
so called, that is to say, completely developed 
quasi-percepts. These commonly assume 
the form of visual or auditory hallucina- 
tions. Like the incomplete hallucinations, 
they may have their starting-point either in 
some disturbance in the peripheral regions 
of the nervous system or in the automatic 
activity of the central structures : or, to use 
the language of Baillarger, we may say that 
they are either “ pyscho-sensorial ” or purely 
“ psychical.” A subjective visual sensation, 
arising from certain conditions in the retina 
and connected portions of the optic nerve, 
may by chance resemble a familiar impression, 
and so be at once interpreted as an effect of a 
particular external object. More frequently, 
however, the automatic activity of the centers 
must be regarded, either in part or altogether, 
as the physiological cause of the phenomenon. 
This is clearly the case when, on the subjec- 
tive side, the hallucination answers to a pre- 
ceding energetic activity of the imagination, 
as in the case of the visionary and the mono- 
maniac. Sometimes, however, as we have 
* See A nnales Mt!dico-Psychologiqucs, tom. vi. p. 
i68, etc., tom. vii. p. i, etc. A PSYCHOLOGICAL STUDY. 
seen, the hallucinatory percept answers to 
previous prolonged acts of perception, leav- 
ing a kind of reverberation in the structures 
concerned; and in this case it is obviously 
impossible to say whether the peripheral or 
central regions (if either) have most to do 
with the hallucination.* 
The classifications of the causes of hallu- 
cination to be met with in the works of pa- 
thologists, bear out the distinction just 
drawn. Griesinger tells us {op. cit., pp. 94, 
95) that the general causes of hallucination 
are: (1) Local disease of the organ of sense; 
(2) a state of deep exhaustion either of mind 
or of body; (3) morbid emotional states, 
such as fear; (4) outward calm and stillness 
between sleeping and waking; and (5) the 
action of certain poisons, as haschisch, opium, 
belladonna. The first cause points pretty 
distinctly to a peripheral origin, whereas the 
others appear to refer mainly, if not exclu- 
sively, to central derangements. Excessive 
fatigue appears to predispose the central 
structures to an abnormal kind of activity, 
and the same effect may be brought about 
by emotional agitation and by the action of 
poisons. The fourth case mentioned here, ab- 
sence of external stimulation, would naturally 
raise the nervous structures to an exceptional 
pitch of excitability. Such a condition would, 
moreover, prove favorable to hallucination 
by blurring the distinction between mental 
image and actual impression. 
Hallucinations of Normal Life.—In normal 
life, perfect hallucinations, in the strict sense 
as distinct from illusions, are comparatively 
rare. Fully developed persistent hallucina- 
tions, as those of Nicolai, the Berlin book- 
seller, and of Mrs. A , the lady cited by 
Sir D. Brewster, in his Letters on Natural 
Magic, point to the presence of incipient 
nervous disorder. In healthy life, on the 
other hand, while everybody is familiar with 
subjective sensations such as flying spots, 
phosphenes, ringing in the ears, few fall into 
the error of seeing or hearing distinct recog- 
nizable objects in the absence of all external 
impressions. In the lives of eminent men 
we read of such phenomena as very occa- 
sional events. Malebranche, for example, is 
said to have heard the voice of God calling 
him. Descartes says that, after a long con- 
finement, he was followed by an invisible 
person, calling him to pursue his search for 
truth. Dr. Johnson narrates that he once 
heard his absent mother calling him. Byron 
tells us that he was sometimes visited by 
specters. Goethe records that he once saw 
an exact counterpart of himself coming 
toward him. Sir Walter Scott is said to 
have seen a phantom of the dead Byron. It 
is possible that all of us are liable to mo- 
mentary hallucinations at times of excep- 
tional nervous exhaustion, though they are 
too fugitive to excite our attention. 
When not brought on by exhaustion or ar- 
tificial means, the hallucinations of the sane 
have their origin in a preternatural power of 
imagination. It is well known that this 
power can be greatly improved by attention 
and cultivation. Goethe used to exercise 
himself in watching for ocular spectra, and 
could at will transform these subjective sen- 
sations into definite forms, such as flowers; 
and Johannes Muller found he had the same 
power* Stories are told of portrait painters 
who could summon visual images of their 
sitters with a vividness equal to that of real- 
ity, and serving all the purposes of their art. 
Mr. Galton’s interesting inquiries into the 
power of “ visualizing ” would appear to 
prove that many people can at will sport on 
the confines of the phantom world of hallu- 
cination. There is good reason to think 
that imaginative children tend to confuse 
mental images and percepts.! 
The Hallucinations of Insanity.—The hal- 
lucinations of the insane are but a fuller 
manifestation of forces that we see at work 
in normal life. Their characteristic is that 
they simulate the form of distinctly present 
objects, the existence of which is not instantlv 
contradicted by the actual surroundings of 
the moment.J The hallucinations have 
their origin partly in subjective sensations, 
which are probably connected with periphe- 
ral disturbances, partly and principally in 
central derangements. § These include pro- 
* That subjective sensation may become the 
starting-point in complete hallucination is shown 
in a curious instance given by Lazarus, and quoted 
by Taine, ofi. cit., vol. i. p. 122, et seq. The Ger- 
man psychologist relates that, on one occasion in 
Switzerland, after gazing for some time on a chain 
of snow-peaks, he saw an apparition of an absent 
friend, looking like a corpse. He goes on to ex- 
plain that this phantom was the product of an 
image of recollection which somehow managed to 
combine itself with the (positive) after-image left 
by the impression of the snow-surface. 
+ For an account of Mr. Galton’s researches, 
see Mind, No. xix. Compare, however, Professor 
Bain’s judicious observations on these results in 
the next number of Mind. The liability of chil- 
dren to take images for percepts, is illustrated by the 
experiences related in a curious little work, Visions. 
by E. H. Clarke, M.D. (Boston, U.S., 1878), pp. 17, 
.46, and 212. 
X A common way of describing the relation of 
the hallucinatory to real objects, is to say that the 
former appear partly to cover and hide the latter. 
§ Griesinger remarks that the forms of the hallu- 
cinations of the insane rarely depend on sense-dis- 
turbances alone. Though these are often thestart- 
ing-point, it is the whole mental complexion of the 
time which gives the direction to the imagination. 
The common experience of seeing rats and mice 
running about during a fit of delirium tremens 
very well illustrates the co-operation of peripheral 
impressions not usually attended to, and possibly 
magnified by the morbid state of sensibility of the 
time (in this case flying spots, muscee volitantes), 
with emotional conditions. (See Griesinger, loc. 
cit., p. 96 ) 
* I have already touched on the resonance of a 
sense-impression when the stimulus has ceased to 
act (see p. 16). The remarks in the text hold good 
of all such after-impressions, in so far as they take 
the form of fully developed percepts. A good ex- 
ample is the recurrence of the images of micro- 
scopic preparations, to which the anatomist is lia- 
ble. (See Lewes, Problems 0/ Life and Mind, 
third series, vol. ii. p. 299.) Since a complete hallu- 
cination is supposed to involve the peripheral re- 
gions of the nerve, the mere fact of shutting the 
eye would not, it is dear, serve as a test of the or- I 
igin of the illusion. ILLUSIONS: 
found emotional changes, which affect the 
ruling mental tone, and exert a powerful in- 
fluence on the course of the mental images. 
The hallucinations of insanity are due to a 
projection of mental images which have, 
owing to certain circumstances, gained a 
preternatural persistence and vividness. 
Sometimes it is the images that have been 
dwelt on with passionate longing before the 
disease, sometimes those which have grown 
most habitual through the mode of daily oc- 
cupation,* and sometimes those connected 
with some incident at or near the time of 
the commencement of the disease. 
In mental disease, auditory hallucinations 
play a part no less conspicuous than visual.! 
Patients frequently complain of having their 
thoughts spoken to them, and it is not un- 
common for them to imagine that they are 
addressed by a number of voices at the same 
time. I 
These auditory hallucinations offer a good 
■opportunity for studying the gradual growth 
of centrally originating hallucinations. In 
the early stages of the disease, the patient 
partly distinguishes his representative from 
his presentative sounds. Thus, he talks of ser- 
mons being composed to him in his head. He 
calls these “ internal voices,” or “ voices of the 
soul.” It is only when the disease gains ground 
and the central irritability increases that these 
audible thoughts become distinctly projected 
as external sounds into more or less definite 
regions of the environment. And it is ex- 
ceedingly curious to notice the different di- 
rections which patients give to these sounds, 
referring them now to a quarter above the 
head, now to a region below the floor, and so 
on.§ 
Range of Sense-Illusions.—And now let us 
glance back to see the path we have tra- 
versed. We set out with an account of per- 
fectly normal perception, and found, even 
here, in the projection of our sensations of 
color, sound, etc., into the environment or to 
the extremities of the organism, something 
which, from the point of view of physical 
science, easily wears the appearance of an in- 
gredient of illusion. 
Waiving this, however, and taking the 
word illusion as commonly understood, we 
find that it begins when the element of imag- 
ination no longer answers to a present real- 
ity or external fact in any sense of this ex- 
pression. In its lowest stages illusion closely 
counterfeits correct perception in the balance 
of the direct factor, sensation, and the indi- 
rect factor, mental reproduction or imagina- 
tion. The degree of illusion increases in 
proportion as the imaginative element gains 
in force relatively to the present impression; 
till, in the wild illusions of the insane, the 
amount of actual impression becomes evanes- 
cent. When this point is reached, the act of 
imagination shows itself as a purely creative 
process, or an hallucination. 
While we may thus trace the progress of 
illusion toward hallucination by means of the 
gradual increase in force and extent of the 
imaginative, or indirect, as opposed to the 
sensuous, or direct, element in perception, 
we have found a second starting-point for 
this movement in the mechanism of sensa- 
tion, involving, as it does, the occasional 
production of “ subjective sensations.” Such 
sensations constitute a border-land between 
the regions of illusion in the narrow sense, 
and hallucination. In their simplest and 
least developed form they may be regarded, 
at least in the case of hearing and sight, as 
partly hallucinatory; and they serve as a 
natural basis for the construction of complete 
hallucinations, or hallucinatory percepts. 
In these different ways, then, the slight, 
scarcely noticeable illusions of normal life 
lead up to the most startling hallucinations 
of abnormal life. From the two poles of the 
higher centers of attention and imagination 
on the one side, and the lower regions of 
nervous action involved in sensation on the 
other side, issue forces which may, under 
certain circumstances, develop into full hal- 
lucinatory percepts. Thus closely is healthy 
attached to morbid mental life. There seems 
to be no sudden break between our most sober 
every-day recognitions of familiar objects and 
the wildest hallucinations of the demented. 
As we pass from the former to the latter, we 
find that there is never any abrupt transition, 
never any addition of perfectly new elements, 
but only that the old elements go on combin- 
ing in ever new proportions. 
The connection between the illusory side 
of our life and insanity may be seen in another 
way. All illusion has as its negative condi- 
tion an interruption of the higher intellectual 
processes, the due control of our mental 
representations by reflection and reason. In 
the case of passive illusions, the error arises 
from our inability to subordinate the sugges- 
tion made by some feature of the present 
* Wundt (Physiologischc Psychologies p. 652) tells 
us of an insane woodman who saw logs of wood on 
all hands in front of the real objects. 
+ It is stated by Baillarger. {Memoires de 1'A ctid- 
drnie Royale de Medicine, tom. xii. p. 273, etc.) that 
while visual hallucinations are more frequent than 
auditory in healthy life, the reverse relation holds 
in disease. At the same time, Griesinger remarks 
(loc. cit., p. 98) that visual hallucinations are rather 
more common than auditory in disease also. This 
is what we should expect from the number of sub- 
jective sensations connected with the peripheral 
organ of vision. The greater relative frequency of 
auditory hallucinations in disease, if made out, 
would seem to depend on the close connection be- 
tween articulate sounds and the higher centers of 
intelligence, which centers are naturally the first to 
be thrown out 'of working order. It is possible,' 
moreover, that auditory hallucinations are quite as 
common as visual in states of comparative health, 
though more easily overlooked. Professor Huxley 
relates that he is liable to auditory though not to 
visual hallucinations. (See Elementary Lessons in 
Physiology, p. 267.) 
t See Baillarger, Memoires de 1'Academic Royale 
de Medicine, tom. xii. p. 273, et seq. 
§ See Baillarger, AnnalesMedico-Psychologiques, 
tom. vi. p. 168 et seq.; also tom. xii. p. 273, et seq. 
Compare Griesinger, op. cit. In a curious work en- 
titled Du Ddmon de Socrate (Paris, 1856), M. Lelut 
seeks to prove that the philosopher’s admonitory 
voice was an incipient auditory hallucination 
symptomic of a nascent stage of mental alienation. A PSYCHOLOGICAL STUDY. 
impression to the result of a fuller inspection 
of the object before us, or of a wider reflec- 
tion on the past. In other words, our minds 
are dominated by the partial and the partic- 
ular, to the exclusion of the total or the 
general. In active illusions, again, the 
powers of judgment and reflection, including 
those of calm perception itself, temporarily 
vacate their throne in favor of imagination. 
And this same suspension of the higher in- 
tellectual functions, the stupefaction of judg- 
ment and reflection made more complete 
and permanent, is just what characterizes 
insanity. 
We may, perhaps, express this point of 
connection between the illusions of normal 
life and insanity bv help of a physiological 
hypothesis. If the nervous system has been 
slowly built up, during the course of human 
history, into its present complex form, it fol- 
lows that those nervous structures and con- 
nections which have to do with the higher 
intellectual processes, or which represent the 
larger and more general relations of our 
experience, have been most recently evolved. 
Consequently, they would be the least deeply 
organized, and so the least stable; that is to 
say, the most liable to be thrown hors de 
combat. This is what happens temporarily 
in the case of the sane, when the mind is held 
fast by an illusion. And, in states of insanity, 
we see the process of nervous dissolution be- 
ginning with the same nervous structures, and 
so taking the reverse order of the process of 
evolution.* And thus, we may say that 
throughout the mental life of the most sane 
of us, these higher and more delicately bal- 
anced structures are constantly in danger of 
being reduced to that state of inefficiency, 
which in its full manifestation is mental 
disease. 
Does this way of putting the subject seem 
alarming? Is it an appalling thought that 
our normal mental life is thus intimately 
related to insanity, and graduates away into 
it by such fine transitions ? A moment’s 
reflection will show that the case is not so 
bad as it seems. It is well to remind our- 
selves that the brain is a delicately adjusted 
organ, which very easily gets disturbed, and 
that the best of us are liable to become the 
victims of absurd illusion if we habitually 
allow our imaginations to be overheated, 
whether by furious passion or by excessive 
indulgence in the pleasures of day-dreaming, 
or in the intoxicating mysteries of spiritual- 
ist seances. But if we take care to keep our 
heads cool and avoid unhealthy degrees of 
mental excitement, we need not be very 
anxious on the ground of our liability to this 
kind of error. As I have tried to show, our 
most frequent illusions are necessarily con- 
nected with something exceptional, either in 
the organism or in the environment. That 
is to say, it is of the nature of illusion in 
healthy conditions of body and mind to be 
something very occasional and relatively un- 
important. Our perceptions may be regarded 
as the reaction of the mind on the impressions 
borne in from the external world, or as a 
process of adjustment of internal mental 
relations to external physical relations. If 
this process is, in the main, a right one, we 
need not greatly trouble, because it is not 
invariably so. We should accept the occa- 
sional failure of the intellectual mechanism 
as an inseparable accompaniment of its gen- 
eral efficiency. 
To this it must be added that many of the 
illusions described above can hardly be called 
cases of non-adaptation at all, since they have 
no relation to the practical needs of life, and 
consequently are, in a general way, unattend- 
ed to. In other cases, again, namely, where 
the precise nature of a present sensation, 
being practically an unimportant matter, is 
usually unattended to, as in the instantaneous 
recognition of objects by the eye under 
changes of illumination, etc., the illusion is 
rather a part of the process of adaptation, 
since it is much more important to recognize 
the permanent object signified by the sensa- 
tion than the precise nature of the present 
sensational “ sign ” itself. 
Finally, it should never be forgotten that 
in normal states of mind there is always the 
possibility of rectifying an illusion. What 
distinguishes abnormal from normal mental 
life is the persistent occupation of the mind 
by certain ideas, so that there is no room for 
the salutary corrective effect of reflection on 
the actual impression of the moment, by 
which we are wont to “orientate,” or take 
our bearings as to the position of things 
about us. In sleep, and in certain artificially 
produced states, much the same thing pre- 
sents itself. Images become realities just 
because they are not instantly recognized as 
such by a reference to the actual surround- 
ings of the moment. But in normal waking 
life this power of correction remains with us. 
We may not exercise it, it is true, and thus 
the illusion will tend to become more or less 
persistent and recurring; for the same law 
applies to true and to false perception: 
repetition makes the process easier. But if 
we only choose to exert ourselves, we can 
always keep our illusions in a nascent or 
imperfectly developed stage. This applies 
not only to those half-illusions into which we 
voluntarily fall, but also to the more irresist- 
ible passive illusions, and those arising from 
an over-excited imagination. Even persons 
subject to hallucinations, like Nicolai of 
Berlin, learn to recognize the unreal character 
of these phantasms. Sir W. Scott tells us, in 
his entertaining work Demonology and Witch- 
craft,, that one of the greatest poets of his 
age, when asked if he believed in ghosts, an- 
swered, “ No, madam, I have seen too many 
of them.” However irresistible our sense- 
illusions may be, so long as we are under the 
sway of particular impressions or mental 
images, we can, when resolved to do so, un- 
deceive ourselves by carefully attending to 
♦This is well brought out by Dr. J. Hughlings 
Jackson, in the papers in Brain, already referred 
to. 36 
ILLUSIONS: 
the actual state of things about us. And in 
many cases, when once the correction is made, 
the illusion seems an impossibility/ By no 
effort of imagination are we able to throw 
ourselves back into the illusory mental condi- 
tion. So long as this power of dispelling the 
illusion remains with us, we need not be 
alarmed at the number and variety of the 
momentary misapprehensions to which we 
are liable. 
A second and more thoughtful view o£- 
dreams, marking a higher grade of intellect- 
ual culture, is that these visions of the night 
are symbolic pictures unfolded to the inner 
eye of the soul by some supernatural being. 
The dream-experience is now, in a sense, 
less real than it was before, since the phan- 
tasms that wear the guise of objective reali-- 
ties are simply images spread out to the 
spirit’s gaze, or the direct utterance of a di- 
vine message. Still, this mysterious contact 
of the mind with the supernatural is regarded 
as a fact, and so the dream assumes the ap. 
pearance of a higher order of experience; 
Its one point of attachment to the experience 
of waking life lies in its symbolic function; 
for the common form which this supernatural 
view assumes is that the dream is a dim pre- 
vision of coming events. Artemidorus, the 
great authority on dream interpretation 
(ioneirocritics) for the ancient world, actually 
defines a-dream as “a motion or fiction of 
the soul in a diverse form signifying either 
good or evil to come ; ” and even a logician 
like Porphyry ascribes dreams to the influ- 
ence of a good demon, who thereby warns us 
of the evils which another and bad demon is 
preparing for us. The same mode of viewing 
dreams is quite common to-day, and many 
who pride themselves on a certain intellect- 
ual culture, and who imagine themselves to be 
free from the weakness of superstition, are 
apt to talk of dreams as of something myste- 
rious, if not distinctly ominous. Nor is it 
surprising that phenomena which at first 
sight look so wild and lawless, should still 
pass for miraculous interruptions of the nat- 
ural order .of events.* 
Yet, in spite of this obvious and impres- 
sive element of the mysterious in dream-life, 
the scientific impulse to illuminate the less, 
known by the better known has long since 
begun to play on this obscure subject. Even 
in the ancient world a writer might here and 
there be found, like Democritus or Aristotle,, 
who was bold enough to put forward a natural 
and physical explanation of dreams. But it 
has been the work of modern science to pro- 
vide something like an approximate solution 
of the problem. The careful study of mental 
life in its intimate union with bodily opera- 
tions, and the comparison of dream-combina 
tions with other products of the imagination, 
normal as well as morbid, have gradually 
helped to dissolve a good part of the mystery 
which once hung like an opaque mist about 
the subject. In this way, our dream-opera- 
tions have been found to have a much closer 
connection with our waking experiences than 
could be supposed on a superficial view. 
The materials of our dreams are seen, when 
closely examined, to be drawn from our wak- 
ing experience. Our waking consciousness 
acts in numberless ways on our dreams, 
and these again in unsuspected ways influence 
CHAPTER VII. 
DREAMS. 
The phenomena of dreams may well seem 
at first sight to form a world of their own, 
having no discoverable links of connection 
with the other facts of human experience. 
First of all, there is the mystery of sleep, 
which quietly shuts all the avenues of sense, 
and so isolates the mind from contact with 
the world outside. To gaze at the motion- 
less face of a sleeper temporarily rapt from 
the life of sight, sound, and movement— 
which, being common to all, binds us together 
in mutual recognition and social action—has 
always something awe-inspiring. This exter- 
nal inaction, this torpor of sense and muscle, 
how unlike to the familiar waking life, with 
its quick responsiveness and its overflowing 
energy! And then, if we look at dreams 
from the inside, we seem to find but the re- 
verse face of the mystery. How inexpressi- 
bly strange does the late night-dream seem 
to a person on waking! He feels he has 
been seeing and hearing things no less real 
than those of waking life; but things which 
belong to an unfamiliar world, an order of 
sights and a sequence of events quite unlike 
those of waking experience; and he asks 
himself in his perplexity where that once 
visited region really lies, or by what magic 
power it was suddenly and for a moment 
created for his vision. In truth, the very 
name of dream suggests something remote 
and mysterious, and w'hen we want to charac- 
terize some impression or scene which by its 
passing strangeness filled us with wonder, 
we naturally call it dream-like. 
Theories of Dreams.—The earliest theories 
respecting dreams illustrate very clearly this 
perception of the remoteness of dream-life 
from waking experience. By the simple 
mind of primitive man this dream-world is 
regarded as similar in its nature or structure 
to our common wrorld, only lying remote 
from this. The savage conceives that when 
he falls asleep, his second self leaves his 
familiar body and journeys forth to unfamil- 
iar regions, where it meets the departed 
second selves of his dead ancestors, and so 
on. From this point of view, the experience 
of the night, though equal in reality to that 
of the day, is passed in a wholly disconnected 
region.* 
* For a fuller account of the different modes of 
dream-interpretation, see my article “ Dream,” in 
the ninth edition of the Encyclopedia Britannica 
* See E. B. Tylor, Primitive Culture, ch. xi.; cf. 
Herbert Spencer, Principles of Sociology, ch. x. A PSYCHOLOGICAL STUDY. 
x>ur waking mental life.* Not only so, it is 
found that the quaint chaotic play of images 
in dreams illustrates mental processes and 
laws which are distinctly observable in wak- 
ing thought. Thus, for example, the appar- 
ent objective reality of these visions has been 
accounted for, without fhe need of resorting 
to any supernatural agency, in the light of a 
vast assemblage of facts gathered from the 
by-ways, so to speak, of waking mental life. 
I need hardly add that I refer to the illusions 
of sense dealt within the foregoing chapters. 
Dreams are to a large extent the semblance 
of external perceptions. Other psychical 
phenomena, as self-reflection, emotional ac- 
tivity, and so on, appear in dream-life, but 
they do so in close connection with these 
quasi-perceptions. The name “ vision,” given 
by old writers to dreams, sufficiently points 
out this close affinitv of the mental phenom- 
ena to sense-perception ; and so far as science 
is concerned, they must be regarded as a pe- 
culiar variety of sense-illusion. Hence the 
appropriateness of studying them in close 
connection with the illusions of perception of 
the waking state. Though marked off by the 
presence of very exceptional physiological 
conditions, they are largely intelligible by 
help of these physiological and psychological 
principles which we have just been consider- 
ing- 
The State of Sleep.—The physiological ex- 
planation of dreams must, it is plain, set out 
’with an account of the condition of the or- 
ganism known as sleep. While there is here 
much that is uncertain, there are some things 
which are fairly well known. Recent physi- 
ological observation has gone to prove that 
during sleep all the activities of the organism 
are appreciably lowered. Thus, for example, 
according to Testa, the pulse falls by about 
cne-fifth. This lowering of the organic func- 
tions appears, under ordinary circumstances, 
to increase toward midnight, after which 
there is a gradual rising. 
The nervous system shares in this general 
depression of the vital activities. The circu- 
lation being slower, the process of reparation 
and nutrition of the nerves is retarded, and 
so their degree of excitability diminished. 
This is clearly seen in the condition of the 
peripheral regions of the nervous system, in- 
cluding the sense-organs, which appear to be 
but very slightly acted on by their customary 
stimuli. 
The nervous centers must participate in 
this lethargy of the system. In other words, 
the activity of the central substance is low- 
ered, and the result of this is plainly seen in 
what is usually thought of as the characteris- 
tic feature of sleep, namely, a transition from 
vigorous mental activity or intense and clear 
consciousness, to comparative inactivity or 
faint and obscure consciousness. The cause 
of this condition of the centers is supposed 
to be the same as that of fhe torpidity of all 
the other organs in sleep, namely, the retar- 
dation of the circulation. But, though there 
is no doubt as to this, the question of the 
proximate physiological conditions of sleep 
is still far from being settled. Whether 
during sleep the blood-vessels of the brain 
are fuller or less full than during waking, is 
still a moot point. Also the qualitative con- 
dition of the blood in the cerebral vessels is 
still a matter of discussion.* 
Since the effect of sleep is to lower central 
activity, the question naturally occurs whether 
the nervous centers are ever rendered inac- 
tive to such an extent as to interrupt the con- 
tinuity of our conscious life. This question 
has been discussed from the point of view of 
the metaphysician, of the psychologist, and of 
the physiologist, and in no case is perfect 
unanimity to.be found. The metaphysical 
question, whether the soul as a spiritual sub- 
stance is capable of being wholly inactive, or 
whether it is not in what seem the moments 
of profoundest unconsciousness partially 
awake—the question so warmly discussed by 
the Cartesians, Leibnitz, etc.—need not de- 
tain us here. 
Of more interest to us are the psycholog- 
ical and the physiological discussions. The 
former seeks to settle the question by help 
of introspection and memory. On the one 
side, it is urged against the theory of unbro- 
ken mental activity, that we remember so lit- 
tle of the lowered consciousness of sleep.t 
To this it is replied that our forgetfulness of 
the contents of dream-consciousness, even if 
this were unbroken, would be fully accounted 
for by the great dissimilarity between dream- 
ing and waking mental life. It is urged, 
moreover, on this side that a sudden rousing 
of a man from sleep always discovers him in 
the act of dreaming, and that this goes to 
prove the uniform connection of dream- 
ing and sleeping. This argument, again, 
may be met by the assertion that our 
sense of the duration of our dreams is 
found to be grossly erroneous; that, owing 
to the rapid succession of the images, the re- 
alization of which would involve a long dura- 
tion, we enormously exaggerate the length 
of dreams in retrospection.! From this it is 
argued that the dream which is recalled on 
our being suddenly awakened may have had 
its whole course during the transition state 
of waking. 
Again, the fact that a man may resolve, on 
going to sleep, to wake at a certain hour, has 
often been cited in proof of the persistence 
of a degree of mental activity even in perfect- 
ly sound sleep. The force of this considera- 
tion, however, has been explained away by 
saying that the anticipation of rising at an 
* For an account of the latest physiological hy- 
potheses as to the proximate cause of sleep, see 
Radestock, op. cit., appendix. 
t Plutarch, Locke, and others give instances of 
people who never dreamt. Lessing asserted of 
himself that he never knew what it was to dream. 
$ The error touched Ion here will be fully dea:* 
with under Illusions of Memory. 
* For a fuller account of the re«.ct:c>.i of dreams 
on waking consciousness, see Pa.d Radestock, 
■Schlaf und Traurn. The subject k vouched on 
iater, under the Illusions 01 Memory. 38 
ILLUSIONS: 
unusual hour necessarily produces a slight 
amount of mental disquietude, which is quite 
sufficient to prevent sound sleep, and there- 
fore to expose the sleeper to the rousing ac- 
tion of faint external stimuli. 
While the purely psychological method is 
thus wholly inadequate to solve the question, 
physiological reasoning appears also to be 
not perfectly conclusive. Many physiolo- 
gists, not unnaturally desirous of upsetting 
what they regard as a gratuitous metaphysic- 
ical hypothesis, have pronounced in favor of 
an absolutely dreamless or unconscious sleep. 
From the physiological point of view, there 
is no mystery in a totally suspended mental 
activity. On the other hand, there is much 
to be said on the opposite side, and perhaps 
it may be contended that the purely physio- 
logical evidence rather points to the conclu- 
sion that central activity, however diminished 
during sleep, always retains a minimum de- 
gree of intensity. At least, one would be 
disposed to argue in this way from the anal- 
ogy of the condition of the other functions of 
the organism during sleep. Possibly this 
modicum of positive evidence may more than 
outweigh any slight presumption against the 
doctrine of unbroken mental activity drawn 
from the negative circumstance that we re- 
member so little of our dream-life* 
Such being the state of physiological 
knowledge respecting the immediate condi- 
tions of sleep, we cannot look for any certain 
information on the nature of that residual 
mode of cerebral activity which manifests 
itself subjectively in dreams. It is evident, 
indeed, that this question can only be fully 
answered when the condition of the brain as 
a whole during sleep is understood. Mean- 
while we must be content with vague hy- 
potheses. 
It may be said, for one thing, that during 
sleep the nervous substance as a whole is less 
irritable than during waking hours. That is 
to say, a greater amount of stimulus is needed 
to produce any conscious result.! This ap- 
pears plainly enough in the case of the periph- 
eral sense-organs. Although these are not, 
as it is often supposed, wholly inactive during 
sleep, they certainly require a more potent 
external stimulus to rouse them to action. 
And what applies to the peripheral regions 
applies to the centers. In truth, it is clearly 
impossible to distinguish between the dimin- 
ished irritability of the peripheral and that 
of the central structures. 
At first sight it seems contradictory to the 
above to say that stimuli which have little 
effect on the centers of consciousness during 
waking life produce an appreciable result in 
sleep. Nevertheless, it will be found that 
this is the case. Thus organic processes 
which scarcely make themselves known to 
the mind in a waking state, may be shown to» 
be the originators of many of our dreams. 
This fact can only be explained on the 
physical side by saying that the special cere- 
bral activities engaged in an act of attention 
are greatly liberated during sleep by the 
comparative quiescence of the external senses. 
These activities, by co-operating with the- 
faint results of the stimuli coming from the 
internal organs, serve very materially to in» 
crease their effect. 
Finally, it is to be observed that, while the 
centers thus respond with diminished energy 
to peripheral stimuli, external and internal, 
they undergo a direct, or “ automatic,” mode- 
of excitation, being roused into activity inde- 
pendently of an incoming nervous impulse. 
This automatic stimulation has been plausibly 
referred to the action of the products of de- 
composition accumulating in the cerebral 
blood-vessels.* It is possible that there is 
something in the nature of this stimulation 
to account for the force and vividness of its- 
conscious results, that is to say, of dreams. 
The Dream State.—Let us now turn to the 
psychic side of these conditions, that is to > 
say, to the general character of the mental 
states known as dreams. It is plain that the 
closing of the avenues of the external senses, 
which is the accompaniment of sleep, will 
make an immense difference in the mental 
events of the time. Instead of drawing its 
knowledge from without, noting its bearings, 
in relation to the environment, the mind will 
now be given over to the play of internal 
imagination. The activity of fancy will, it is 
plain, be unrestricted by collision with exter- 
nal fact. The internal mental life will ex® 
pand in free picturesque movement. 
To say that in sleep the mind is given over 
to its own imaginings, is to say that the 
mental life in these circumstances will reflect 
the individual temperament and mental his- 
tory. For the play of imagination at any 
time follows the lines of our past experience 
more closely than would at first appear, and 
being colored with emotion, will reflect the 
predominant emotional impulses of the indi- 
vidual mind. Hence the saying of Heraclitus, 
that, while in waking we all have a common 
world, in sleep we have each a world of our 
own. 
This play of imagination in sleep is further- 
ed by the peculiar attitude of attention. 
When asleep the voluntary guidance of at- 
tention ceases; its direction is to a large 
extent determined by the contents of the 
mind at the moment. Instead of holding the 
images and ideas, and combining them ac- 
cording to some rational end, the attention 
relaxes its energies and succumbs to the force 
of imagination. And thus, in sleep, just as 
in the condition of reverie or day-dreaming, 
there is an abandonment of the fancy to its 
own wild ways. 
It follows that the dream-state will not 
* For a very full, fair, and thoughtful discussion 
of this whole question, see Radestock, op. cit., ch. 
iv. 
t This may be technically expressed by saying 
that the liminal intensity (Schwelle) is raised during 
sleep. 
* See Wundt, Physiologische Psychologic, pp. 188-* 
IQI. A PSYCHOLOGICAL STUDY. 
appear to the mind as one of fancy, but as 
one of actual perception, and of contact with 
present reality. Dreams are clearly illusory, 
and, unlike the illusions of waking life, are 
complete and persistent.* And the reason 
of this ought now to be clear. First of all, 
the mind during sleep wants what M. Taine 
calls the corrective of a present sensation. 
When awake under ordinary circumstances, 
any momentary illusion is at once set right 
by a new act of orientation. The superior 
vividness of the external impression cannot 
leave us in any doubt, when calm and self- 
possessed, whether our mental images answer 
to present realities or not. On the other 
hand, when asleep, this reference to a fixed 
objective standard is clearly impossible. 
Secondly, we may fairly argue that the men- 
tal images of sleep approximate in character 
to external impressions. This they do to 
some extent in point of intensity, for, in spite 
of the diminished excitability of the centers, 
the mode of stimulation which occurs in 
sleep may, as I have hinted, involve an ener- 
getic cerebral action. And, however this be, 
it is plain that the image will gain a preter- 
natural force through the greatly narrowed 
range of attention. When the mind of the 
sleeper is wholly possessed by an image or 
group of images, and the attention kept tied 
down to these, there is a maximum re-enforce- 
ment of the images. But this is not all. 
When the attention is thus held captive by 
the image, it approximates in character to an 
external impression in another way. In our 
waking state, when our powers of volition are 
intact, the external impression is character- 
ized by its fixity or its obdurate resistance to 
our wishes. On the other hand, the mental 
image is fluent, accommodating, and disap- 
pears and reappears according to the direction 
of our volitions. In sleep, through the sus- 
pension of the higher voluntary power of 
attention, the mental image seems to lord it 
over our minds just as the actual impression 
of waking life. 
This much may suffice, perhaps, by way of 
a general description of the sleeping and 
dreaming state. Other points will make' 
themselves known after we have studied the 
contents and structure of dreams in detail. 
Dreams are commonly classified (e.g., by 
Wundt) with hallucinations, and this rightly, 
since, as their common appellation of “vis- 
ion ” suggests, they are for the most part the 
semblance of percepts in the absence of exter- 
nal impressions. At the same time, recent 
research goes to show that in many dreams 
something answering to the “external im- 
pression ” in waking perception is the start- 
ing-point. Consequently, in order to be as 
accurate as possible, I shall divide dreams 
into illusions (in the narrow sense) and hallu- 
cinations. 
Dream-Illusions. ■— By dream-illusions I 
mean those dreams which set out from some 
peripheral nervous stimulation, internal or 
external. That the organic processes of di- 
gestion, respiration, etc., act as stimuli to the 
i centers in sleep is well known. Thus, 
J David Hartley assigns as the second great 
source of dreams “ states of the body.” * But 
| it is not so well known to what an extent our 
dreams may be influenced by stimuli acting on 
! the exterior sense-organs. Let us first glance 
at the action of such external stimuli. 
Action of External Stimuli.—During sleep 
the eyes are closed, and consequently the ac- 
tion of external light on the retina impeded. 
Yet it is found that even under these circum- 
stances any very bright light suddenly intro- 
duced is capable of stimulating the optic 
fibers, and of affecting consciousness. The 
most common form of this is the effect of 
bright moonlight, and of the early sun’s rays. 
Krauss tells a funny story of his having once, 
when twenty-six years old, caught himself, on 
waking, in the act of stretching out his arms 
toward what his dream-fancy had pictured as 
the image of his mistress. When fully awake,' 
this image resolved itself into the full moon.t 
It is not improbable, as Radestcck remarks, 
that the rays of the sun or moon are answera- 
ble for many of the dreams of celestial glory 
which persons of a highly religious tempera- 
ment are said to experience. 
External sounds, when not sufficient to rouse 
the sleeper, easily incorporate themselves 
into his dreams. The ticking of a watch, 
the stroke of a clock, the hum of an insect, 
the song of a bird, the patter of rain, w’as com- 
mon stimuli to the dream-phantasy. M. Alf. 
Maury tells us, in his interesting account of 
the series of experiments to which he submit- 
ted himself in order to ascertain the result 
of external stimulation on the mind during 
sleep, that when a pair of tweezers was made 
to vibrate near his ear, he dreamt of bells, 
the tocsin, and the events of June, 18484 
Most of us, probably, have gone through the 
experience of impolitely falling asleep when 
some one was reading to us, and of having 
dream-images suggested by the sounds that 
were still indistinctly heard. Schemer gives 
an amusing case of a youth who was permit- 
ted to whisper his name into the ear of his 
obdurate mistress, the consequence of which 
was that the lady contracted a habit of dream- 
ing about him, which led to a felicitous 
change of feeling on her part.§ 
The two lower senses, smell and taste, 
seem to play a less important part in the pro- 
duction of dream-illusions. Radestock says 
that the odor of flowers in a room easily 
leads to visual images of hot-houses, per- 
fumery shops, and so on ; and it is probable 
that the contents of the mouth may occasion- 
ally act as a stimulus to the organ of taste, 
* There is, indeed, sometimes an undertone of 
critical reflection, which is sufficient to produce a 
feeling- of uncertainty and bewilderment, and in 
very rare cases to amount to a vague consciousness 
that the mental experience is a dream. 
* Observations on Man, Part I. ch. iii. sec. 5. 
+ Quoted by Radestock, op. cit., p. no. 
X Le Sommeil et tes Roves, P.I132, et seq. 
$ Das Leben des Traumes, p. 369. Other in- 
stances are related by Beattie and Abercrombie. ILLUSIONS: 
and so give rise to corresponding dreams. | 
As Radestock observes, these lower sensa-1 
tions do not commonly make known their 
quality to the sleeper’s mind. They become 
transformed at once into visual, instead of 
into olfactory or gustatory percepts. That is 
to say, the dreamer does not imagine him- 
self smelling or tasting, but seeing an object. 
The contact of objects with the tactual or- 
gan is one of the best recognized causes of 
dreams. M. Maury found that when his lips 
were tickled, his dream-fancy interpreted the 
impression as of a pitch plaster being torn off 
his face. An unusual pressure on any part of 
the body, as, for example, from contact with 
a fellow-sleeper, is known to give rise to a 
well marked variety of dream. Our own 
limbs may even appear as foreign bodies to 
our dream-imagination, when through pres- 
sure they become partly paralyzed. Thus, 
on one occasion, I awoke from a miserable 
dream, in which I felt sure I was grasping 
somebody’s hand in bed, and I was racked by 
terrifying conjectures as to who it might be. 
When fully awake, I discovered that I had 
been lying on my right side, and clasping the 
wrist of the right arm (which had been ren- 
dered insensible by the pressure of the body) 
with the left hand. 
In close connection with these stimuli of 
pressure are those of muscular movement, 
whether unimpeded or impeded. We need 
not enter into the difficult question how far 
the “muscular sense ” is connected with the 
activity of the motor nerves, and how far 
with sensory fibers attached to the muscular 
or the adjacent tissues. Suffice it to say that 
an actual movement, a resistance to an at- 
tempted movement, or a mere disposition to 
movement, whether consequent on a surplus 
of motor energy or on a sensation of discom- 
fort or fatigue in the part to be moved, some- 
how or other makes itself known to our 
minds, even when we are deprived of the as- 
sistance of vision. And these feelings of 
movement, impeded or unimpeded, are com- 
mon initial impulses in our dream-experiences. 
It is quite a mistake to suppose that dreams 
are built up out of the purely passive sensa- 
tions of sight and hearing. A close observa- 
tion will show that in nearly every dream we 
imagine ourselves either moving among the 
objects we perceive or striving to move when 
some weighty obstacle obstructs us. All of 
us are familiar with the common forms of 
nightmare, in which we strive hopelessly to 
flee from some menacing evil, and this 
dream-experience, it may be presumed, fre- 
quently comes from a feeling of strain in the 
muscles, due to an awkward disposition of 
the limbs during sleep. The common dream- 
illusion of falling down a vast abyss is plausi- 
bly referred by Wundt to an involuntary ex- 
tension of the foot of the sleeper. 
Action of Internal Stimuli,—Let us now 
pass from the action of stimuli lying outside 
the organism, to that of stimuli lying with- 
in the peripheral regions of the sense-organs. 
1 have already spoken of the influence of 
subjective sensations of sight, hearing, etc., 
on the illusions of waking life, and it is now 
to be added that these sensations play an im- 
portant part in our dream-life.. Johannes 
Muller lays great prominence on the part 
taken by ocular spectra in the production of 
dreams. As he observes, the apparent rays 
of light, light-patches, mists of light, and so 
on, due to changes of blood-pressure in the 
retina, only manifest themselves clearly when 
the eyes are closed and the more powerful 
effect of the external stimulus cut off. These 
subjective spectra come into prominence in 
the sleepy condition, giving rise to what M. 
Maury calls “ hallucinations hypnagogiques,” 
and which he regards (after Gruithuisen) as 
the chaos out of which the dream-cosmos is 
evolved.* They are pretty certainly the 
starting-point in those picturesque dreams in 
which figure a number of bright objects, such 
as beautiful birds, butterflies, flowers, or an- 
gels. 
That the visual images of our sleep do 
often involve the peripheral regions of the 
organ of sight, seems to be proved by the 
singular fact that they sometimes persist 
after waking. Spinoza and Jean Paul Rich- 
ter both experienced this survival of dream- 
images. Still more pertinent is the fact that 
the effects of retinal fatigue are producible 
by dream-images. The physiologist Gruith- 
uisen had a dream, in which the principal 
feature was a violet flame, and which left be- 
hind it, after waking, for an appreciable du- 
ration, a complementary image of a yellow 
spot.! 
Subjective auditory sensations appear to 
be much less frequent causes of dream-illu- 
sions than corresponding visual sensations. 
Yet the rushing, roaring sound caused by the 
circulation of the blood in the ear is, proba- 
bly, a not uncommon starting-point in dreams. 
With respect to subjective sensations of 
smell and taste, there is little to be said. 
On the other hand, subjective sensations due 
to varying conditions in the skin are a very 
frequent exciting cause of dreams. Varia- 
tions in the state of tension of the skin, 
brought about by alteration of position, 
changes in the character of the circulation, 
the irradiation of heat to the skin or the loss 
of the same, chemical changes—these are 
known to give rise to a number of familiar 
sensations, including those of tickling, itching, 
burning, creeping, and so on; and the effects 
of these sensations are distinctly traceable in 
our dreams. For example, the exposure of 
a part of the body through a loss of the bed- 
clothes is a frequent excitant of distressing 
dreams. A cold foot suggests that the 
sleeper is walking over snow or ice. On the 
other hand, if the cold foot happens to touch 
a warm part of the body, the dream-fancy 
* Le Sommeil ct les Reves< p. 42, et seg. 
t Beitrdge zur Physiognosie und Hautognosie, 
p. 256. For other cases see H. Meyer, Physiologic 
der Nervettfaser, p. 309 ; and Strtimpell, Die Natur 
und Rntstehungder Prauine, p. 125. A PSYCHOLOGICAL STUDY. 
41 
constructs images of walking on burning lava, 
and so on. 
These sensations of the skin naturally con- 
duct us to the organic sensations as a whole ; 
that is to say, the feelings connected with the 
varying condition of the bodily organs. 
These include the feelings which arise in 
connection with, the processes of digestion, 
respiration, and circulation, and the condi- 
-tion of various organs according to their state 
■of nutrition, etc. During our waking life 
these organic feelings coalesce for the most 
part, forming as the “ vital sense ” an obscure 
background for our clear discriminative con- 
-sciousness, and only come forward into this 
region when very exceptional in character, as 
when respiration or digestion is impeded, or 
when we make a special effort of attention to 
single them out.* When we are asleep, 
however, and the avenues of external per- 
ception are closed, they assume greater 
prominence and distinctness. The centers, 
no longer called upon to react on stimuli 
coming from without the organism, are free 
to react on stimuli coming from its hidden 
recesses. So important a part, indeed, do 
these organic feelings take in the dream- 
drama, that some writers are disposed to re- 
gard them as the great, if not the exclusive, 
■cause of dreams. Thus, Schopenhauer held 
that the excitants of dreams are impressions 
received from the internal regions of the or- 
ganism through the sympathetic nervous 
system.! 
It is hardly necessary, perhaps, to give 
many illustrations of the effect of such organ- 
ic sensations on our dreams. Among the 
most common provocatives of dreams are 
sensations connected with a difficulty in 
breathing, due to the closeness of the air or 
to the pressure of the bed-clothes on the 
mouth. J. Borner investigated the influence 
of these circumstances by covering with the 
bed-clothes the mouth and a part of the nos- 
trils of persons who were sound asleep. 
This was followed by a protraction of the act 
of breathing, a reddening of the face, efforts 
to throw off the clothes, etc. On being 
roused, the sleeper testified that he had ex- 
perienced a nightmare, in which a horrid 
animal seemed to be weighing him down.! 
Irregularity of the heart’s action is also a 
frequent cause of dreams. It is not improba- 
ble that the familiar dream-experience of 
flying arises from disturbances of the respira- 
tory and circulatory movements. 
Again, the effects of indigestion, and more 
particularly stomachic derangement, on 
dreams are too well known to require illus- 
tration. It may be enough to allude to the 
famous dream which Hood traces to an ex- 
cessive indulgence at supper. It is known 
that the varying condition of the organs of 
secretion influences our dream-fancy in a 
number of ways. 
Finally, it is to be observed that an injury 
done to any part of the organism is apt to 
give rise to appropriate dream-images. In 
this way, very slight disturbances which 
would hardly affect waking consciousness 
may make themselves felt during sleep. 
Thus, for example, an incipient toothache has 
been known to suggest that the teeth are 
being extracted.* 
It is worth observing that the interpreta- 
tion of these various orders of sensations by 
the imagination of the dreamer takes very 
different forms according to the person’s 
character, previous experience, ruling emo- 
tions, and so on. This is what is meant by 
saying that during sleep every man has a 
world of his own, whereas, when awake, he 
shares in the common world of perception. 
Dream-Exaggeration.—It is to be noticed, 
further, that this interpretation of sensation 
during sleep is uniformly a process of exag- 
geration.! The exciting causes of the feel- 
ings of discomfort, for example, are always 
absurdly magnified. The reason of this 
seems to be that, owing to the condition of 
the mind during sleep, the nature of the sen- 
sation in not clearly recognizable. Even in 
the case of familiar external impressions, 
such as the sound of the striking of a clock, 
there appears to be wanting that simple proc- 
ess of reaction by which, in a waking con- 
dition of the attention, a sense-impression is 
instantly discriminated and classed. In sleep, 
as in the artificially induced hypnotic condi- 
tion, the slighter differences of quality among 
sensations are not clearly recognized. The 
activity of the higher centers, which are con- 
cerned in the finer processes of discrimina- 
tion and classification, being greatly reduced, 
the impression may be said to come before 
consciousness as something novel and unfa- 
miliar. And just as we saw that in waking 
life novel sensations agitate the mind, and 
so lead to an exaggerated mode of interpre- 
tation, so here we see that what is unfamiliar 
disturbs the mind, rendering it incapable of 
calm attention and just interpretation. 
This failure to recognize the real nature of 
an impression is seen most conspicuously in 
the case of the organic sensations. As I 
have remarked, these constitute for the most 
part, in waki»g life, an undiscriminated mass 
of obscure feeling, of which we are only con- 
scious as the mental tone of the hour. And 
* A very clear and full account of these organic 
■sensations, or common sensations, has recently ap- 
peared from the pen of A. Horwicz in the Viertel- 
jak rssck rift fur wissenschaftliche Philosophies iv. 
Jahrgang 3tes Heft. 
t Schopenhauer uses this hypothesis in order to 
■account for the apparent reality of dream-illusions. 
He thinks these internal sensations may be trans- 
formed by the “ intuitive function ” of the brain 
(by means of the “forms” of space, time, etc.) 
into quasi-realities, just as well as the subjective 
sensations of light, sound, etc., which arise in the 
organs of sense in the absence of external stimuli, 
f See Versuck iiber das Geistersehen : lVerke,\ol. v. 
p. 244, et seq.) 
i Das A Ipdriicken. pp. 8, 9, 27. 
* It is this fact which justifies writers in assign- 
ing a prognostic character to dreams. 
t A part of the apparent exaggeration in our 
dream-experiences may be retrospective, and due 
to the effect of the impression of wonder which 
they leave behind them. (See Striimpell, Die 
Natur und Entstehung der Traume.) ILLUSIONS: 
42 
in the few instances in which we do attend to 
them separately, whether through their ex- 
ceptional intensity or in consequence of an 
extraordinary effort of discriminative atten- 
tion, we can only be said to perceive them, 
that is, recognize their local origin, very 
vaguely. Hence, when asleep, these sensa- 
tions get very oddly misinterpreted. 
The localization of a bodily sensation in 
waking life means the combination of a tact- 
ual and a visual image with the sensation. 
Thus, my recognition of a twinge of tooth- 
ache as coming from a certain tooth, involves 
representations of the active and passive sen- 
sations which touching and looking at the 
tooth would yield me. That is to say, the 
feeling instantly calls up a compound mental 
image exactly answering to a visual percept. 
This holds good in dream-interpretation too ; 
the interpretation is effected by means of a 
visual image. But since the feeling is only 
very vaguely recognized, this visual image 
does not answer to the bodily part concerned. 
Instead of this, the fancy of the dreamer con- 
structs some visual image which bears a vague 
resemblance to the proper one, and is gener- 
ally, if not always, an exaggeration of this in 
point of extensive magnitude, etc. For ex- 
ample, a sensation arising from pressure on 
the bladder, being dimly connected with the 
presence of a fluid, calls up an image of a 
flood, and so on. 
This mode of dream-interpretation has 
by some writers been erected into the typi- 
cal mode, under the name of dream-symbol- 
ism. Thus Schemer, in his interesting 
though somewhat fanciful work, Das Lebendes 
Traumes, contends that the various regions of 
the body regularly disclose themselves to the 
dream-fancy under the symbol of a building 
or group of buildings; a pain in the head 
calling up, for example, the image of spiders 
on the ceiling, intestinal sensations exciting 
an image of a narrow alley, and so on. Such 
theories are clearly an exaggeration of the 
fact that the localization of our bodily sen- 
sations during sleep is necessarily imperfect.* 
In many cases the image called up bears 
on its objective side no discoverable resem- 
blance to that of the bodily region or the ex- 
citing cause of the sensation. Here the ex- 
planation must be looked for in the subject- 
ive side of the sensation and mental image, 
that is to say, in their emotional quality, as 
pleasurable or painful, distressing, quieting, 
etc. It is to be observed, indeed, that in 
natural sleep, as in the condition known as 
hypnotism, while differences of specific quality 
in the sense-impressions are lost, the broad 
difference of the pleasurable and the painful 
is never lost. It is, in fact, the subjective 
emotional side of the sensation that uniformly 
forces itself into consciousness. This being 
so, it follows that, speaking generally, the 
sensations of sleep, both external and inter- 
nal, or organic, will be interpreted by what 
G. H. Lewes has called “an analogy of feel- 
ing; ” that is to say, by means of a mental 
image having some kindred emotional charac- 
ter or coloring. 
Now, the analogy between the higher emo- 
tional and the bodily states is a very close 
one. A sensation of obstruction in breathing 
has its exact analogue in a state of mental 
embarrassment, a sensation of itching its 
counterpart in mental impatience, and so on. 
And since these emotional experiences are 
deeper and fuller than the sensations, the 
tendency to exaggerate the nature and causes 
of these last would naturally lead to an in- 
terpretation of them by help of these experi- 
ences. In addition to this, the predominance 
of visual imagery in sleep would aid this 
transformation of a bodily sensation into an 
emotional experience, since visual percep- 
tions have, as their accompaniments of 
pleasure and pain, not sensations, but emo- 
tions.* 
Since in this vague interpretation of bodily 
sensation the actual impression is obscure, 
and not taken up as an integral part into the 
percept, it is evident that we cannot, strictly 
speaking, call the process an imitation of an 
act of perception, that is to say, an illusion. 
And since, moreover, the visual image by 
which the sensation is thus displaced appears 
as a present object, it would, of course, be al- 
lowable to speak of this as an hallucination. 
This substitution of a more or less analogous 
visual image for that appropriate to the sen- 
sation forms, indeed, a transition from dream- 
illusion, properly so called, to dream-hallu- 
cination. 
Dream Hallucinations.—On the physical 
side, these hallucinations answer to cerebral 
excitations which are central or automatic, 
not depending on movements transmitted 
from the periphery of the nervous system. 
Of these stimulations some appear to be di- 
rect, and due to unknown influences exerted 
by the state of nutrition of the cerebral ele- 
ments, or the action of the contents of the 
blood-vessels on these elements. 
Effects of Direct Central Stimulation.— 
That such action does prompt a large num- 
ber of dream-images may be regarded as 
fairly certain. First of all, it seems impossi- 
ble to account for all the images of dream- 
fancy as secondary phenomena connected by 
links of association with the foregoing classes, 
of sensation. However fine and invisible 
many of the threads which hold together our 
ideas may be, they will hardly explain the 
profusion and picturesque variety of dream- 
imagery. Secondly, we are able in certain 
cases to infer with a fair amount of certainty 
that a dream-image is due to such central 
stimulation. The common occurrence that 
we dream of the more stirring events, the 
* I was on one occasion able to observe this proc- 
ess going on in the transition from waking to 
sleeping. I partly fell asleep when suffering from 
toothache. Instantly the successive throbs of pain 
transformed themselves into a sequence of visible 
movements, which I can only vaguely describe as 
the forward strides of some menacing adversary. 
* Cf. Radestock, op. cit., pp. 131, 132. A PSYCHOLOGICAL STUDY. 
anxieties and enjoyments of the preceding 
day, appears to show that when the cerebral 
elements are predisposed to a certain kind of 
activity, as they are after having been en- 
gaged for some time in this particular work, 
they are liable to be excited by some stimulus 
brought directly to bear on them during 
sleep. And if this is so, it is not improbable 
that many of the apparently forgotten images 
of persons and places which return with such 
vividness in dreams are excited by a mode of 
stimulation which is for the greater part con- 
fined to sleep. I say “ for the greater part,” 
because even in our indolent, listless moments 
of waking existence such seemingly forgotten 
ideas sometimes return as though by a spon- 
taneous movement of their own and by no 
discoverable play of association. 
It may be well to add that this immediate 
revival of impressions previously received by 
the brain includes not only the actual percep- 
tions of waking life, but also the ideas de- 
rived from others, the ideal fancies supplied 
by works of fiction, and even the images 
which our unaided waking fancy is wont to 
shape for itself. Our daily conjectures as to 
the future, the communications to us by 
others of their thoughts, hopes, and fears,— 
these give rise to numberless vague fugitive 
images, any one of which may become dis- 
tinctly revived in sleep.* This throws light 
on the curious fact that we often dream of ex- 
periences and events quite unlike those of 
our individual life. Thus, for example, the 
common construction by the dream-fancy of 
the experience of flight in mid-air, and the 
creation of those weird forms which the ter- 
ror of a nightmare is wont to bring in its 
train, seem to point to the past action of wak- 
ing fancy. To imagine one’s self flying when 
looking at a bird is probably a common 
action with all persons, at least in their ear- 
lier years, and images of preternaturally hor- 
rible beings are apt to be supplied to most of 
us some time during life by nurses or by 
books. 
Indirect Central Stimulation.—Besides 
these direct central stimulations, there are 
others which, in contradistinction, may be 
called indirect, depending on some previous 
excitatign. These are, no doubt, the condi- 
tions of a very large number of our dream- 
images. There must, of course, be some pri- 
mary cerebral excitation, whether that of a 
present peripheral stimulation, or that which 
has been termed central and spontaneous; 
but when once this first link of the imaginative 
chain is supplied, Other links may be added 
in large numbers through the operation of the 
forces of association. One may, indeed, 
| safely say that the large proportion of the 
contents of every dream arise in this way. 
The very simplest type of dream excited by 
a present sensation contains these elements. 
To take an example, I once dreamt, as a con- 
sequence of the loud barking of a dog, that a 
dog approached me when lying down, and be- 
gan to lick my face. Here the play of the asso- 
ciative forces was apparent: a mere sensation 
of sound called up the appropriate visual im- 
age, this again the representation of a charac- 
teristic action, and so on. So it is with the 
dreams whose first impulse is some central or 
spontaneous excitation. A momentary sight 
of a face or even the mention of a name dur- 
ing the preceding day may give the start to 
dream-activity; but all subsequent members 
of the series of images owe their revival to a 
tension, so to speak, in the fine threads which 
bind together, in so complicated a way, our 
impressions and ideas. 
Among the psychic accompaniments of 
these central excitations visual images, as al- 
ready hinted, fill the most conspicuous place. 
Even auditory images, though by no means 
absent, are much less numerous than visual. 
Indeed, when there are the conditions for the 
former, it sometimes happens that the audi- 
tory effect transforms itself into a visual ef- 
fect. An illustration of this occurred in my 
own experience. Trying to fall asleep by 
means of the well-known device of counting,, 
I suddenly found myself losing my hold on 
the faint auditory effects, my imagination 
transforming them into a visual spectacle, un- 
der the form of a path of light stretching 
away from me, in which the numbers ap- 
peared under the grotesque form of visible 
objects, tumbling along in glorious confusion. 
Next to these visual phantasms, certain mo- 
tor hallucinations seem to be most prominent 
in dreams. By a motor hallucination, I 
mean the illusion that we are actually mov- 
ing when there is no peripheral excitation of 
the motor organ. Just as the centers con- 
cerned in passive sensation are susceptible of 
central stimulation, so are the centers con- 
cerned in muscular sensation. A mere im- 
pulse in the centers of motor innervation (if 
we assume these to be the central seat of the 
muscular feelings) may suffice to give rise to 
a complete representation of a fully executed 
movement. And thus in our sleep we seem 
to walk, ride, float, or fly. 
The most common form of motor halluci- 
nation is probably the vocal. In the social 
encounters which make up so much of our 
sleep-experience, we are wont to be very 
talkative. Now, perhaps, we find ourselves 
zealously advocating some cause, now very 
fierce in denunciation, now very amusing in 
witty repartee, and so on. This imagination 
of ourselves as speaking, as distinguished 
from that of hearing others talking, must, it 
is dear, involve the excitation of the struct- 
ures engaged in the production of the mus- 
cular feelings which accompany vocal action, 
as much as, if not more than, the auditory 
centers. And the frequency of this kind of 
* Even the “ unconscious impressions ” of waking 
hours, that is to say, those impressions which are so 
fugitive as to leave no psychical trace behind, may 
thus rise into the clear light of consciousness during 
sleep. Maury relates a curious dream of his own, 
in which there appeared a figure that seemed quite 
strange to him, though he afterward found that 
ne must have been in the habit of meeting the 
original in a street through which he was accus- 
tomed to walk (loc. cit., p. 124). ILLUSIONS: 
■dream-experience may be explained, like that 
•of visual imagery, by the habits of waking 
life. The speech impulse is one of the most 
deeply rooted of all our impulses, and one 
which has been most frequently exercised in 
vwaking life. 
Combmation of Dream-Elements.—It is 
tcommonly said that dreams are a grotesque 
dissolution of all order, a very chaos and 
'whirl of images without any discoverable 
connection. On the other hand, a few writ- 
ers claim for the mind in sleep a power of 
arranging and grouping its incongruous ele- 
ments in definite and even life-like pictures. 
Each of these views is correct within certain 
.limits; that is to say, there are dreams in 
■which the strangest disorder seems to prevail, 
.and others in which one detects the action of 
a central control. Yet, speaking generally, 
sequences of dream-images will be found to 
be determined by certain circumstances and 
laws, and so far not to be haphazard or 
wholly chaotic. We have now to inquire into 
the laws of these successions; and, first of 
all, we may ask how far the known laws of 
association, together with the peculiar con- 
ditions of the sleeping state, are able to ac- 
count for the various modes of dream-combi- 
nation. We have already regarded mental 
.association as furnishing a large additional 
store of dream-imagery; we have now to 
consider it as explaining the sequences and 
concatenations of our dream-elements. 
Incoherence of Dreams.—First of all, then, 
let us look at the chaotic and apparently law- 
less side of dreaming, and see whether any 
clue is discoverable to the center of this laby- 
rinth. In the case of all the less elaborately 
ordered dreams, in which sights and sounds 
appear to succeed one another in the wildest 
dance (which class of dreams probably be- 
longs to the deeper stages of sleep), the 
. mind may with certainty be regarded as 
purely passive, and the mode of sequence 
may be referred to the action of association 
complicated by the ever-recurring introduc- 
tion of new initial impulses, both peripheral 
and central. These are the dreams in which 
we are conscious of being perfectly passive, 
either as spectators of a strange pageant, or 
as borne away by some apparently extraneous 
force through a series of the most diverse 
experiences. The flux of images in these 
dreams is very much the same as that in cer- 
tain waking conditions, in which we relax at- 
tention, both external and internal, and yield 
ourselves wholly to the spontaneous play 
of memory and fancy. 
It is plain at a glance that the simultaneous 
concurrence of wholly disconnected initial 
impulses will serve to impress a measure 
of disconnectedness on our dream-images. 
From widely remote parts of the organism 
there come impressions which excite each its 
peculiar visual or other image according as 
its local origin or its emotional tone is the 
more distinctly present to consciousness. 
Nowit is a subjective ocular sensation sug- 
gesting a bouquet of lovely flowers, and close 
on its heels comes an impression from the 
organs of digestion suggesting all manner of 
obstacles ; and so our dream-fancy plunges 
from a vision of flowers to one of dreadful 
demons. 
Let us now look at the way in which the 
laws of association working on the incongru- 
ous elements thus cast up into our dream-con- 
sciousness, will serve to give a yet greater ap- 
pearance of disorder and confusion to our 
dream-combinations. According to these 
laws, any idea may, under certain circumstan- 
ces, call up another, if the corresponding im- 
pressions have only once occurred together, 
or if the ideas have any degree of resemb- 
lance, or, finally, if only they stand in marked 
contrast with one another. Any accidental 
coincidence of everts, such as meeting a per- 
son at a particular foreign resort, and any 
insignificant resemblance between objects, 
sounds, etc., may thus supply a path, so to 
speak, from fact to dream-fancy. 
In our waking states these innumerable 
paths of association are practically closed by 
the supreme energy of the coherent groups 
of impressions furnished us from the world 
without through our organs of sense, and also 
by the volitional control of internal thought 
in obedience to the pressure of practical 
needs and desires. In dream-life both of 
these influences are withdrawn, so that deli- 
cate threads of association, which have no 
chance of exerting their pull, so to speak, in 
our waking states, now make known their 
hidden force. Little wonder, then, that the 
filaments which bind together these dream- 
successions should escape detection, since 
even in our waking thought we so often fail 
to see the connection which makes us pass 
in recollection from a name to a visible scene 
or perhaps to an emotional vibration. 
It is worth noting that the origin of an as- 
sociation is often to be looked for in one of 
those momentary half-conscious acts of wak- 
ing imagination to which reference has al- 
ready been made. A friend, for example, 
has been speaking to us of some common 
acquaintance, remarking on his poor health. 
The language calls up, vaguely, a visual rep- 
resentation of the person sinking in health 
and dying. An association will thus be 
formed between this person and the idea of 
death. A night or two after, the image of 
this person somehow recurs to our dream- 
fancy, and we straightway dream that we are 
looking at his corpse, watching his funeral, 
and so on. The links of the chain which 
holds together these dream-images were 
really forged, in part, in our waking hours, 
though the process was so rapid as to escape 
our attention. It may be added, that in 
many cases where a juxtaposition of dream- 
images seems to have no basis in waking 
life, careful reflection will occasionally bring 
to light some actual conjunction of impres- 
sions so momentary as to have faded from 
our recollection. 
We must remember, further, how great an 
apparent disorder will invade our imagina- A PSYCHOLOGICAL STUDY. 
45 
tive dream-life when the binding force of re- 
semblance has unchecked play. In waking 
thought we have to connect things according 
to their essential resemblances, classifying ob- 
jects and events for purposes of knowledge 
or action according to their widest or their 
most important points of similarity. In sleep, 
on the contrary, the slightest touch of resem- 
blance may engage the mind and affect the 
direction of fancy. In a sense we may be 
said, when dreaming, to discover mental affin- 
ities between impressions and feelings, includ- 
ing those subtle links of emotional analogy 
of which I have already spoken. This effect 
is well illustrated in a dream recorded by M. 
Maury, in which he passed from one set of 
images to another through some similarity of 
names, as that between corps and cor. Such 
a movement of fancy would, of course, be pre- 
vented in full waking consciousness by a pre- 
dominant attention to the meaning of the 
sounds. 
It will be possible, I think, after a habit of 
analyzing one’s dreams in the light of pre- 
ceding experience has been formed, to dis- 
cover in a good proportion of cases some hid- 
den force of association which draws together 
the seemingly fortuitous concourse of our 
dream-atoms. That we should expect to do 
so in every case is unreasonable, since, owing 
to the numberless fine ramifications which 
belong to our familiar images, many of the 
paths of association followed by our dream- 
fancy cannot be afterward retraced. 
To illustrate the odd way in which our im- 
ages get tumbled together "through the action 
of occult association forces, I will record a 
dream of my own. I fancied I was at the 
house of a distinguished literary acquaint- 
ance, at her usual reception hour. I ex- 
pected the friends I was in the habit of meet- 
ing there. Instead of this, I saw a number 
of commonly dressed people having tea. My 
hostess came up and apologized for having 
asked me into this room. It was, she said, a 
tea-party which she prepared for poor people 
at sixpence a head. After puzzling over this 
dream, I came to the conclusion that the 
missing link was a verbal one. A lady who 
is a connection of my friend, and bears the 
same name, assists her sister in a large kind 
of benevolent scheme. I may add that I had 
not, so far as I could recollect, had occasion 
very recently to think of this benevolent 
friend, but I had been thinking of my literary 
friend in connection with her anticipated re- 
turn to town. 
In thus seeking to trace, amid the super- 
ficial chaos of dream-fancy, its hidden con- 
nections, I make no pretense to explain why 
in any given case these particular paths of 
association should be followed, and more 
particularly why a slender thread of associa- 
tion should exert a pull where a stronger 
cord fails to do so. To account for this, it 
would be necessary to call in the physiologi- 
cal hypothesis that among the nervous ele- 
ments connected with a particular element, a, 
already excited, some,-as m and n, are at the 
moment, owing to the state of their nutrition 
or their surrounding influences, more power- 
fully predisposed to activity than other ele- 
ments, as b and c. 
The subject of association naturally con- 
ducts us to the second great problem in the 
theory of dreams—the explanation of the or- 
der in which the various images group them- 
selves in all our more elaborate dreams. 
Coherence of Dreams.—A fully developed 
dream is a complex of many distinct illusory 
sense-presentations : in this respect it differs 
from the illusions of normal waking life, 
which are for the most part single and isolat- 
ed. And this complex ui quasi-presenta- 
tions appears somehow or other to fall to- 
gether into one whole scene or series of 
events, which, though it may be very incon- 
gruous and absurdly impossible from a wak- 
ing point of view, nevertheless makes a sin- 
gle object for the dreamer’s internal vision,, 
and has a certain degree of artistic unity. 
This plastic force, which selects and binds 
together our unconnected dream-images, has 
frequently been referred to as a mysterious 
spiritual faculty, under the name of “ creative 
fancy.” Thus Cudworth remarks, in his 
Treatise concerning Eternal and Immutable 
Morality: “That dreams are many times 
begotten by the phantastical power of the 
soul itself ... is evident from the orderly 
connection and coherence of imaginations 
which many times are continued in a long 
chain or series.” One may find a good deal 
of mystical writing on the nature and activity 
of this faculty, especially in German litera- 
ture. The explanation of this element of or- 
ganic unity in dreams is, it may be safely said, 
the crux in the science of dreams. That the 
laws of psychology help us to understand the 
sequences of dream-images, we have seen. 
What we have now to ask is whether these 
laws throw any light on the orderly grouping 
of the elements so brought up in conscious- 
ness in the form of a connected experience. 
It is to be remarked at the outset that a 
singular kind of unity is sometimes given to 
our dream-combinations by a total or partial 
coalescence of different images. The con- 
ditions of such coalescence have been re- 
ferred to already* Simultaneous impres- 
sions or images will always tend to coalesce 
with a force which varies directly as the de- 
gree of their similarity. Sometimes this co- 
alescence is instantaneous and not made 
known to consciousness. Thus, Radestock 
suggests that if the mind of the sleeper is- 
simultaneously invaded by an unpleasant 
sensation arising out of some disturbance of 
the functions of the skin, and a subjective- 
visual sensation, the resulting mental image 
may be a combination of the two, under the 
form of a caterpillar creeping over the bodily 
surface. And the coalescence may be pre- 
pared by sub-conscious operations of waking 
imagination. Thus, for example, I once 
spoke about the cheapness of hares to a mem- 
* See p. 16. 46 
ILLUSIONS: 
ber of my family, who somewhat grimly sug- 
gested that they were London cats. I did 
not dwell on the idea, but the following 
night I dreamt that I saw a big hybrid 
creature, half hare, half cat, sniffing about a 
cottage. As it stood on its hind legs and 
took a piece of food from a window-ledge, I 
became sure that it was a cat. Here it is 
plain that the cynical observation of my rel- 
ative* had, at the moment, partially excited 
an image of this feline hare. In some 
dreams, again, we may become aware of the 
process of coalescence, as when persons who 
at one moment were seen to be distinct ap- 
pear to our dream-fancy to run together in 
some third person. 
A very similar kind of unification takes 
place between sequent images under the form 
of transformation. When two images fol- 
low one another closely, and have anything 
in common, they readily assume the form of 
a transmutation. There is a sort of over- 
lapping of the mental images, and so an ap- 
pearance of continuity produced in some re- 
spects analogous to that which arises in the 
wheel-of-life (thaumatrope) class of sense-il- 
lusions. This would seem to account for 
the odd transformations of personality which 
not unfrequently occur in dreams, in which a 
person appears, by a kind of metempsycho- 
sis, to transfer his physical ego to another, 
and in which the dreamer’s own bodily phan- 
tom plays similar freaks. And the same 
principle probably explains those dissolving- 
view effects which are so familiar an accom- 
paniment of dream-scenery.* 
But passing from this exceptional kind of 
unity in dreams, let us inquire how the heter- 
■ ogeneous elements of our dream-fancy be- 
come ordered and arranged when they pre- 
serve their separate existence. If we look 
closely at the structure of our more finished 
dreams, we find that the appearance of har- 
mony, connectedness, or order, may be given 
in one of two ways. There may, first of all, 
be a subjective harmony, the various images 
being held together by an emotional thread. 
Or there; may, secondly, be an objective har- 
mony, the parts of the dream, though answer- 
ing to no particular experiences of waking 
life, bearing a certain resemblance to our ha- 
bitual modes of experience. Let us inquire 
into the way in which each kind of order is 
brought about. 
Lyrical Element in Dreams.—The only 
unity that belongs to many of our dreams is 
a subjective emotional unity. This is the 
basis of harmony in lyrical poetry, where the 
succession of images turns mainly on their 
emotional coloring. Thus, the images that 
float before the mind of the Poet Laureate, 
in his In Memoriam, clearly have their link 
of connection in their common emotional 
tone, rather than in any logical continuity. 
Dreaming has been likened to poetic com- 
position, and certainly many of our dreams 
are built upon a groundwork of lyrical feel- 
ing. They might be marked off, perhaps, as 
our lyrical dreams. 
The way in which this emotional force acts 
in these cases has already been hinted at. 
We have seen that the analogy of feeling is a 
common link between dream-images. Now, 
if any shade of feeling becomes fixed and 
dominant in the mind, it will tend to control 
all the images of the time, allowing certain 
congruous ones to enter, and excluding 
others.* If, for example, a feeling of dis- 
tress occupies the mind, distressing images 
will have the advantage in the struggle for 
existence which goes on in the world of mind 
as well as in that of matter. We may say 
that attention, which is here wholly a passive 
process, is controlled by the emotion of the 
time, and bent in the direction of congruent 
or harmonious images. 
Now a ground-tone of feeling of a certain 
complexion, answering to the sum of sensa- 
tions arising in connection with the different 
organic processes of the time, is a very fre- 
quent foundation of our dream-structure. So- 
frequent is it, indeed, that one might almost 
say there is no dream in which it is not one 
great determining factor. The analysis of a 
very large number of dreams has convinced 
me that traces of this influence are discover- 
able in a great majority. 
I will give a simple illustration of this lyr- 
ical type of dream. A little girl of about 
four years and three-quarters went with her 
parents to Switzerland. On their way she 
was taken to the cathedral at Strasburg, and 
saw the celebrated clock strike, and the fig- 
ures of the Apostles come out, etc. In Swit- 
zerland she stayed at Gimmelwald, near 
Miirren, opposite a fine mass of snowy mount- 
ains. One morning she told her father that 
she had had “such a lovely dream.” She 
fancied she was on the snow-peaks with her 
nurse, and walked on to the sky. There 
came out of the sky “ such beautiful things,” 
just like the figures of the clock. This vision 
of celestial things was clearly due to the fact 
that both the clock and the snow-peaks touch- 
ing the blue sky had powerfully excited her 
imagination, filling her with much the same 
kind of emotion, namely, wonder, admiration, 
and longing to reach an inaccessible height. 
Our feelings commonly have a gradual rise 
and fall, and the organic sensations which so 
often constitute the emotional basis of our 
lyrical dreams generally have stages of in- 
creasing intensity. Moreover, such a per- 
sistent ground-feeling becomes re-enforced by 
the images which it sustains in consciousness. 
Hence a certain crescendo character in our 
emotional dreams, or a gradual rise to some 
culminating point or climax. 
This phase of dream can be illustrated 
from the experience of the same little girl. 
When just five years old, she was staying at 
Hampstead, near a church which struck the 
* See what was said respecting the influence of a 
dominant emotional agitation on the interpretation 
of actual sense impressions. 
* See Maury, loc. cit., p. 146. A PSYCHOLOGICAL STUDY. 
47 
hours somewhat loudly. One morning she 
related the following dream to her father (I 
use her own language). The biggest bells 
in the world were ringing; when this was 
over the earth and houses began to tumble 
to pieces; all the seas, rivers, and ponds 
flowed together, and covered all the land 
with black water, as deep as in the sea where 
the ships sail; people were drowned; she her- 
self flew above the water, rising and falling, 
fearing to fall in; she then saw her mamma 
drowned, and at last flew home to tell her 
papa. The gradual increase of alarm and 
distress expressed in this dream, having its 
probable cause in the cumulative effect of 
the disturbing sound of the church bells, 
must be patent to all. 
The following rather comical dream illus- 
trates quite as clearly the growth of a feeling 
of irritation and vexation, probably connected 
with the development of some slightly de- 
composing organic sensation. I dreamt I 
was unexpectedly called on to lecture to a 
class of young women, on Herder. I began 
hesitatingly, with some vague generalities 
about the Augustan age of German litera- 
ture, referring to the three well-known names 
of Lessing, Schiller, and Goethe. Immedi- 
ately my sister, who suddenly appeared in 
the class, took me up, and said she thought 
there was a fourth distinguished name belong- 
ing to this period. I was annoyed at the in- 
terruption, but said, with a feeling of triumph, 
“ I suppose you mean Wieland?” and then 
appealed to the class whether there were not 
twenty persons who knew the names I had 
mentioned to one who knew Wieland’s name. 
Then the class became generally disorderly. 
My feeling of embarrassment gained in 
depth. Finally, as a climax, several quite 
young girls, about ten years and less, came 
and joined the class. The dream broke off 
abruptly as I was in the act of taking these 
children to the wife of an old college tutor, 
to protest against their admission. 
It is worth noting, perhaps, that in this 
evolution of feeling in dreaming the quality 
of the emotion may vary within certain lim- 
its. One shade of feeling may be followed 
by another and kindred shade, so that the 
whole dream still preserves a degree, though 
a less obvious degree, of emotional unity. 
Thus, for example, a lady friend of mine 
once dreamt that she was in church, listening 
to a well-known novelist of the more earnest 
sort, preaching. A wounded soldier was 
brought in to be shot, because he was mor- 
tally wounded, and had distinguished himself 
by his bravery. He was then shot, but not 
killed, and rolling over in agony, exclaimed, 
“ How long ! ” The development of an ex- 
treme emotion of horror out of the vague 
feeling of awe which is associated with a 
church, gives a curious interest to this 
dream. 
Verisimilitude in Dreams.—I must not 
dwell longer on this emotional basis of 
dreams, but pass to the consideration of the 
second and objective kind of unity which 
characterizes many of our more elaborate 
dream-performances. In spite of all that is 
fitful and grotesque in dream-combination, it 
still preserves a distant resemblance to our 
actual experience. Though no dream repro- 
duces a particular incident or chain of inci- 
dents in this experience, though the dream- 
fancy invariably transforms the particular ob- 
jects, relations, and events of waking life, it 
still makes the order of our daily experience 
its prototype. It fashions its imaginary 
world on the model of the real. Thus, ob- 
jects group themselves in space, and act on 
one another conformably to these perceived 
space-relations; events succeed one another 
in time, and are often seen to be connected; 
men act from more or less intelligible motives, 
and so on. In this way, though the dream- 
fancy sets at naught the particular relations 
of our experience, it respects the general and 
constant relations. How are we to account 
for this ? 
It is said by certain philosophers that this 
superposition of the relations of space, time, 
causation, etc., on the products of our dream- 
fancy is due to the fact that all experience 
arises by a synthesis of mental forms with the 
chaotic master of sense-impressions. These 
philosophers allow, however, that all particu- 
lar connections are determined by experience. 
Accordingly, what we have to do here is to 
inquire how far this scientific method of ex- 
plaining mental connections by facts of ex- 
perience will carry us. In other words, we 
have to ask what light can be thrown on 
these tendencies of dream-imagination by as- 
certained psychological laws, and more partic- 
ularly by what are known as the laws of asso- 
ciation. 
These laws tell us that of two mental phe- 
nomena which occur together, each will tend 
to recall the other whenever it happens to be 
revived. On the physiological side, this 
means that any two parts of the nervous 
structures which have acted together become 
in some way connected, so that when one 
part begins to work the other will tend to 
work also. But it is highly probable that a 
particular structure acts in a great many dif- 
ferent ways. Thus it may be stimulated by 
unlike modes of stimuli, or it may enter into 
very various connections with other struct- 
ures. What will follow from this ? One 
consequence would appear to be that there 
will be developed an organic connection be- 
tween the two structures, of such a kind that 
whenever one is excited the other will be dis- 
posed to act somehow and anyhow, even 
when there is nothing in the present mode of 
activity of the first structure to determine the 
second to act in some one definite way, in 
other words, when this mode of activity is, 
roughly speaking, novel. 
Let me illustrate this effect in one of the 
simplest cases, that of the visual organ. 
If, when walking out on a dark night, a few 
points in my retina are suddenly stimulated 
by rays of light, and I recognize some lumi- 
nous object in a corresponding direction, I am 48 
ILLUSIONS: 
prepared to see something above and below, 
to the right and to the left of this object. 
Why is this ? There may from the first have 
been a kind of innate understanding among 
contiguous optic fibers, predisposing them to 
such concerted action. But however this be, 
this disposition would seem to have been 
largely promoted by the fact that, through- 
out my experience the stimulation of any 
retinal point has been connected with that of 
adjoining points, either simultaneously by 
some second object, or successively by the 
same object as the eye moves over it, or as 
the object itself moves across the field of vis- 
ion. 
When, therefore, in sleep any part of the 
optic centers is excited in a particular way, 
and the images thus arising have their corre- 
sponding loci in space assigned to them, 
there will be a disposition to refer any other 
visual images which happen at the moment 
to arise in consciousness to adjacent parts of 
space. The character of these other images 
will be determined by other special conditions 
of the moment; their locality or position in 
space will be determined by this organic con- 
nection. We may, perhaps, call these tend- 
encies to concerted action of some kind gen- 
eral associative dispositions. 
Just as there are such dispositions to 
united action among various parts of one or- 
gan of sense, so there may be among differ- 
ent organs, which are either connected origi- 
nally in the infant organism, or have commu- 
nications opened up by frequent co-excitation 
of the two. Such links there certainly are 
between the organs of taste and smell, and 
between the ear and the muscular system in 
general, and more particularly the vocal or- 
gan.* A new odor often sets us asking how 
the object would taste, and a series of sounds 
commonly disposes us to movement of some 
kind or another. How far there maybe finer 
threads of connection between other organs, 
such as the eye and the ear, which do not be- 
tray themselves amid the stronger forces of 
waking mental life, one cannot say. What- 
ever their number, it is plain that they will 
exert their influence within the comparatively 
narrow limits of dream-life, serving to impress 
a certain character on the images which hap- 
pen to be called up by special circumstances, 
and giving to the combination a slight meas- 
ure of congruity. Thus, if I were dreaming 
that I heard some lively music, and at the 
same time an image of a friend was anyhow 
excited, my dream-fancy might not improba- 
bly represent this person as performing a se- 
quence of rhythmic movements, such as those 
of riding, dancing, etc. 
A narrower field for these general associa- 
tive dispositions may be found in the tend- 
ency, on the reception of an impression of a 
given character, to look for a certain kind of 
second impression; though the exact nature 
of this is unknown. Thus, for example, the 
form and color of a new flower suggests a 
scent, and the perception of a human form is 
accompanied by a vague representation of 
vocal utterances. These general tendencies 
of association appear to me to be most po- 
tent influences in our dream-life. The many 
strange human forms which float before our 
dream-fancy are apt to talk, move, and be- 
have like men and women in general, how- 
ever little they resemble their actual proto- 
types, and however little individual consist- 
ency of character is preserved by each of 
them. Special conditions determine what 
they shall say or do; the general associative 
disposition accounts for their saying or doing 
something. 
We thus seem to find in the purely passive 
processes of association some ground for 
that degree of natural coherence and rational 
order which our more mature dreams com- 
monly possess. These processes go far to* 
explain, too, that odd mixture of rationality 
with improbability, of natural order and in- 
congruity, which characterizes our dream- 
combinations. 
Rational Construction in Dreams.—Neverthe- 
less, I quite agree with Herr Volkelt that as- 
sociation, even in the most extended meaning, 
cannot explain all in the shaping of our 
dream-pictures. The “ phantastical power ” 
which Cudworth talks about clearly includes- 
something besides. It is an erroneous sup- 
position that when we are dreaming there 
is a complete suspension of the voluntary 
powers, and consequently an absence of all 
direction of the intellectual processes. This 
supposition, which has been maintained by 
numerous writers, from Dugald Stewart 
downward, seems to be based on the fact 
that we frequently find ourselves in dreams 
striving in vain to move the whole body or a 
limb. But this only shows, as M. Maury re- 
marks in the work already referred to, that 
our volitions are frustrated through the iner- 
tia of our bodily organs, not that these voli- 
tions do not take place. In point of fact, the 
dreamer, not to speak of the somnambulist, 
is often conscious of voluntarily going 
through a series of actions. This exercise of 
volition is shown unmistakably in the well- 
known instances of extraordinary intellect- 
ual achievements in dreams, as Condillac’s 
composition of a part of his Cours d’Etudes. 
No one would maintain that a result of this 
kind was possible in the total absence of in- 
tellectual action carefully directed by the will. 
And something of this same control shows 
itself in all our more fully developed 
dreams. 
One manifestation of this voluntary ac- 
tivity in sleep is to be found in those efforts 
of attention which not unfrequently occur. I 
have remarked that, speaking roughly and in 
relation to the waking condition, the state of 
sleep is marked by a subjection of the powers 
of attention to the force of the mental images 
* It is proved experimentally that the ear has a 
much closer organic connection with the vocal organ 
than the eye has. Donders found that the period 
required for responding vocally to a sound signal is 
less than that required for responding in the same 
way to a light signal. A PSYCHOLOGICAL STUDY. 
present to consciousness. Yet something re- 
sembling an exercise of voluntary attention 
sometimes happens in sleep. The intellect- 
ual feats just spoken of, unless, indeed, they 
are referred to some mysterious unconscious 
mental operations, clearly involve a measure 
of volitional guidance. All who dream fre- 
quently are occasionally aware on awaking 
of having greatly exercised their attention 
on the images presented to them during sleep. 
I myself am often able to recall an effort to 
see beautiful objects, which threatened to 
disappear from my field of vision, or to catch 
faint receding tones of preternatural sweet- 
ness; and some dreamers allege that they 
are able to retain a recollection of the feel- 
ing of strain connected with such exercise of 
attention in sleep. 
The main function of this voluntary atten- 
tion in dream-life is seen in the selection of 
those images which are to pass the threshold 
of clear consciousness. I have already 
spoken of a selective action brought about 
by the ruling emotion. In this case, the at- 
tention is held captive by the particular feel- 
ing of the moment. Also a selective process 
goes on in the case of the action of those as- 
sociative dispositions just referred to. But in 
each case of these cases the action of select- 
ive attention is comparatively involuntary, 
passive, and even unconscious, not having 
anything of the character of a conscious 
striving to compass some end. Besides this 
comparatively passive play of selective atten- 
tion, there is an active play, in which there is 
a conscious wish to gain an end; in other 
words, the operation of a definite motive. 
This motive maybe described as an intellect- 
ual impulse to connect and harmonize what 
is present to the mind. The voluntary kind 
of selection includes and transcends each of 
the involuntary kinds. It has as its result 
an imitation of that order which is brought 
about by what I have called the associative 
dispositions, only it consciously aims at this 
result. And it is a process controlled by a 
feeling, namely, the intellectual sentiment of 
consistency, which is not a mode of emotion- 
al excitement enthralling the will, but a calm 
motive, guiding the activities of attention. 
It thus bears somewhat the same relation to 
the emotional selection already spoken of, 
as dramatic creation bears to lyrical compo- 
sition. 
This process of striving to seize some con- 
necting link, or thread of order, is illustrated 
whenever, in waking life, we are suddenly 
brought face to face with an unfamiliar scene. 
When taken into a factory, we strive to ar- 
range the bewildering chaos of visual impres- 
sions under some scheme, by help of which 
we are said to understand the scene. So, if 
on entering a room w»are plunged in medias 
res of a lively conversation, we strive to find 
a clue to the discussion. Whenever the 
meaning of a scene is not at once clear, and 
especially whenever there is an appearance 
of confusion in it, we are conscious of a 
painful feeling of perplexity, which acts 
as a strong motive to ever-renewed atten- 
tion.* 
In touching on this intellectual impulse to 
connect the disconnected, we are, it is plain, 
approaching the question of the very founda- 
tions of our intellectual structure. That 
there is this impulse firmly rooted in the ma- 
ture mind nobody can doubt; and that it 
manifests itself in early life in the child’s re- 
curring “ Why ? ” is equally clear. But how 
we are to account for it, whether it is to be 
viewed as a mere result of the play of asso- 
ciated fragments of experience, or as some- 
thing involved- in the very process of the as- 
sociation of ideas itself, is a question into 
which I cannot here enter. 
What I am here concerned to show is that 
the search for consistency and connection in 
the manifold impressions of the moment is a 
deeply rooted habit of the mind, and 011c 
which is retained in a measure during sleep. 
When, in this state, our minds are invaded 
by a motley crowd of unrelated images, there 
results a disagreeable sense of confusion; 
and this feeling acts as a motive to the at- 
tention to sift out those products of the 
dream-fancy which may be made to cohere. 
When once the foundations of a dream-action 
are laid, new images must to some extent fit 
in with this ; and here there is room for the 
exercise of a distinct impulse to order the 
chaotic elements of dream-fancy in certain 
forms. The perception of any possible re- 
lation between one of the crowd of new im- 
ages ever surging above the level of obscure 
consciousness, and the old group at once 
serves to detain it. The concentration of at- 
tention on it, in obedience to this impulse to 
seek for an intelligible order, at once intensi- 
fies it and fixes it, incorporating it into the 
series of dream-pictures. 
Here is a dream which appears to illus- 
trate this impulse to seek an intelligible or- 
der in the confused and disorderly. After 
being occupied with correcting the proofs of 
my volume on Pessimism, I dreamt that my 
book was handed to me by my publisher, 
fully illustrated with colored pictures. The 
frontispiece represented the fantastic figure 
of a man gesticulating in front of a ship, 
from whieh he appeared to have just stepped. 
My publisher told me it was meant for 
Hamlet, and I immediately reflected that 
this character had been selected as a con- 
crete example of the pessimistic tendency. 
I may add that, on awaking, I was distinctly 
aware of having felt puzzled when dreaming, 
and of having striven to read a meaning into 
the dream. 
The rationale of this dream seems to me to 
be somewhat as follows. The image of the 
completed volume represented, of course, a 
recurring anticipatory image of waking life. 
The colored plates were due probably to 
subjective optical sensations simultaneously 
* On the nature of this impulse, as illustrated in 
waking and in sleep, see the article by Delbceuf, 
“ Le Sommeil et les Reves,” in the Revue Philoso- 
fhique, June, 1880, p.636. ILLUSIONS: 
excited, which were made to fit in (with or 
without an effort of voluntary attention) with 
tlje image of the book under the form of il- 
lustrations. But this stage of coherency did 
not satisfy the mind, which, still partly con- 
fused by the incongruity of colored plates in 
a philosophic work, looked for a closer con- 
nection. The image of Hamlet was natural- 
ly suggested in connection with pessimism. 
The effort to discover a meaning in the pict- 
ures led to the fusion of this image with one 
of the subjective spectra, and in this way the 
idea of a Hamlet frontispiece probably arose. 
The whole process of dream-construction 
is clearly illustrated in a curious dream re- 
corded by Professor Wundt.* Before the 
housejs a funeral procession : it is the burial 
of a friend, who has in reality been dead for 
some time past. The wife of the deceased 
bids him and an acquaintance who happens 
to be with him go to the other side of the 
street and join the procession. After she 
has gone away, his companion remarks to 
him, “ She only said that because the cholera 
rages over yonder, and she wants to keep 
this side of the street to herself.” Then 
comes an attempt to flee from the region of 
the cholera. Returning to his house, he 
finds the procession gone, but the street 
strewn with rich nosegays; and he further 
observes crowds of men who seem to be fu- 
neral attendants, and who, like himself, are 
hastening to join the procession. These are, 
oddly enough, dressed in red. When hurry- 
ing on, it occurs to him that he has forgotten 
to take a wreath for the coffin. Then he 
wakes up with beating of the heart. 
The sources of this dream are, according 
to Wundt, as follows. First of all, he had, 
on the previous day, met the funeral proces- 
sion of an acquaintance. Again, he had read 
of cholera breaking out in a certain town. 
Once more, he had talked about the particu- 
lar lady with this friend, who had narrated 
facts which clearly proved her selfishness. 
Th e hastening to flee from the infected neigh- 
borhood and to overtake the procession was 
prompted by the sensation of heait-beating. 
Finally, the crowd of red bier-followers, and 
the profusion of nosegays, owed their origin 
to subjective visual sensations, the “ light- 
chaos ” which often appears in the dark. 
Let us now see for a moment 
various elements may have become fused 
into a connected chain of events. First of 
all, it is clear that this dream is built up on 
a foundation of a gloomy tone of feeling, 
arising, as it would seem, from an irregulari- 
ty of the heart’s action. -Secondly, it owes 
its special structure and its air of a connect- 
ed sequence of events, to those tendencies, 
passive and active, to order the chaotic of 
which I have been speaking. Let us try to 
trace this out in detail. 
To begin with, we may suppose that the 
image of the procession occupies the dream- 
er’s mind. From quite another source the 
image of the lady enters consciousness, bring- 
ing with it that of her deceased husband and 
of the friend who has recently been talking 
about her. These new elements adapt them- 
selves to the scene, partly by the passive 
mechanism of associative dispositions, and 
partly, perhaps, by the activity of voluntary 
selection. Thus, the idea of the lady’s hus- 
band would naturally recall the fact of his 
death, and this would fall in with the pre-ex- 
isting scene under the form of the idea that 
he is the person who is now being buried. 
The next step is very interesting. The image 
of the lady is associated with the idea of self- 
ish motives. This would tend to suggest a 
variety of actions, but the one which becomes 
a factor of the dream is that which is spe- 
cially adapted to the pre-existing represen- 
tations, namely, of the procession on the 
further side of the street, and the cholera 
(which last, like the image of the funeral, is, 
we may suppose, due to an independent cen- 
tral excitation). That is to say, the request 
of the lady, and its interpretation, are a re- 
sultant of a number of adaptative or assimi- 
lative actions, under the sway of a strong de- 
sire to connect the disconnected, and a lively 
activity of attention. Once more, the feeling 
of oppression of the heart, and the subjective 
stimulation of the optic nerve, might suggest 
numberless images besides those of anxious 
flight and of red-clad men and nosegays; 
they suggest these, and not others, in this 
particular case, because of the co-operation 
of the impulse of consistency, which, setting 
out with the pre-existing mental images, se- 
lects from among many tendencies of repro- 
duction those which happen to chime in with 
the scene. 
The A'ature of Dream-Intelligence.—It must 
not be supposed that this process of welding 
together the chaotic materials of our dreams 
is ever carried out with anything like the 
clear rational purpose of which we are con- 
scious when seeking, in waking life, to 
comprehend some bewildering spectacle. 
At best it is a vague longing, and this long- 
ing, it may be added, is soon satisfied. There 
is, indeed, something almost pathetic in the 
facility with which the dreamer’s mind can 
be pacified with the least appearance of a 
connection. Just as a child’s importunate 
“ Why ? ” is often silenced by a ridiculous 
caricature of an explanation, so the dream- 
er’s intelligence is freed from its distress by 
the least semblance of a uniting order. 
It thus remains true with respect even to 
our most coherent dreams, that there is a 
complete suspension, or at least a consider- 
able retardation, of the highest operations of 
judgment and thought; also a great enfeeble- 
ment, to say the least*of it, of those senti- 
ments such "as the feeling of consistency and 
the sense of the absurd which are so inti- 
mately connected with these higher intellect- 
ual operations. 
In order to illustrate how oddly our seem- 
ingly rational dreams caricature the opera- 
tions of waking thought, I may, perhaps, be 
* Physiologische Psychologie. p. 660, A PSYCHOLOGICAL STUDY. 
allowed to record two of my own dreams, of 
which I took careful note at the time. 
On the first occasion I went “ in my dream ” 
to the “ Stores ” in August, and found the 
place empty. A shopman brought me some 
large fowls. I asked their price, and he an- 
swered, “Tenpence a pound.” I then asked 
their weight, so as to get an idea of their to- 
tal cost, and he replied, “Forty pounds.” 
Not in the least surprised, I proceeded to 
calculate their cost: 40 X 10 = 400 4- 12 = 
But, oddly enough, I took this quotient 
as pence, just as though I had not already 
divided by 12, and so made the cost of a fowl 
to be 2s. gd., which seemed to me a fair 
enough price. 
In my second dream I was at Cambridge, 
among a lot of undergraduates. I saw a 
coach diive up with six horses. Three un- 
dergraduates got out of the coach. I asked 
them why they had so many horses, and 
they said, “ Because of the luggage.” I then 
said, “ The luggage is much more than the 
undergraduates. Can you tell me how to ex- 
press this in mathematical symbols? This 
is the way: if vr is the weight of an under- 
graduate, then x -(- xn represents the weight 
of an undergraduate and his luggage to- 
gether.” I noticed that this sally was re- 
ceived with evident enjoyment.* 
We may say, then, that the structure of 
our dreams, equally with the fact of their 
completely illusory character, points to the 
conclusion that during sleep, just as in the 
moments of illusion in waking life, there is 
a deterioration of our intellectual life. The j 
highest intellectual activities answering to 1 
the least stable nervous connections are im- | 
peded, and what of intellect remains corre- 
sponds to the most deeply organized connec- 
tions. 
In this way, our dream-life touches that 
childish condition of the intelligence which 
marks the decadence of old age and the en- 
croachments of mental disease. The parallel- 
ism between dreams and insanity has been 
pointed out by most writers on the subject. 
Kant observed that the madman is a dreamer 
awake, and more recently Wundt has re- i 
marked that, when asleep, we “ can experi- i 
ence nearly all the phenomena which meet j 
us in lunatic asylums.” The grotesqueness 
of the combinations, the lack of all judgment 
as to consistency, fitness, and probability, 
are common characteristics of the short night- 
dream of the healthy and the long day-dream 
of the insane.* 
But one great difference marks off the two 
domains. When dreaming, we are still sane, 
and shall soon prove our sanity. After all, 
the dream of the sleeper is corrected, if not 
so rapidly as the illusion of the healthy waker. 
As soon as the familiar stimuli of light and 
sound set the peripheral sense-organs in ac- 
tivity, and call back the nervous system to its 
complete round of healthy action, the illu- 
sion disappears, and we smile at our alarms 
and agonies, saying, “ Behold, it was a 
dream 1 ” 
On the practical side, the illusions and 
hallucinations of sleep must be regarded as 
comparatively harmless. The sleeper, in 
healthy conditions of sleep, ceases to be an 
agent, and the illusions which enthral his 
brain have no evil practical consequences. 
They may, no doubt, as we shall see in a 
future chapter, occasionally lead to a subse- 
quent confusion of fiction and reality in wak- 
I ing recollection. But with the exception of 
| this, their worst effect is probably the linger- 
ing sense of discomfort which a “ nasty 
dream ” sometimes leaves with us, though 
this may be balanced by the reverberations 
of happy dream-emotions which sometimes 
follow us through the day. And however 
this be, it is plain that any disadvantages 
thus arising are more than made good by the 
consideration that our liability to these noc- 
turnal illusions is connected with the need of 
j that periodic recuperation of the higher 
| nervous structures which is a prime condition 
j of a vigorous intellectual activity, and so of 
! a triumph over illusion dui ing waking life. 
For these reasons dreams may properly be 
classed with the illusions of normal or 
healthy life, rather than with those of disease. 
They certainly lie nearer this region than the 
very similar illusions of the somnambulist, 
which with respect to their origin appear to 
be more distinctly connected with a patholog- 
ical condition of the nervous system, and 
! which with respect to their' practical conse- 
j quences may easily prove so disastrous. 
After-Dreams.—In concluding this account 
| of dreams, I would call attention to the im- 
j portance of the transition states between 
I sleeping and waking, in relation to the pro- 
duction of sense-illusion. And this point 
may be touched on here all the more appro- 
priately, since it helps to bring out the close 
relation between waking and sleeping illu- 
sion. The mind does not pass suddenly and 
at a bound from the condition of dream-fancy 
to that of waking perception. I have already 
had occasion to touch on the “ hypnagogic 
state,” that condition of somnolence or 
“ sleepiness ” in which external impressions 
cease to act, the internal attention is relaxed, 
and the weird imagery of sleep begins to un- 
fold itself. And just as there is this an*ici- 
51 
* I may, perhaps, observe, after giving two 
dreams whicn have to do with mathematical oper- 
ations, that, though I was very fond of them in my 
college days, I have long ceased to occupy myself 
with these processes. I would add, by way of re- 
deeming my dream-intelligence from a deserved 
charge of silliness, that I once performed a respect- 
able intellectual feat when asleep. I put together 
the riddle, “ What might a wooden ship say when 
her side was stove in? Tremendous!” (Tree- 
mend-us). I was aware of having tried to improve 
on the form of this pun. I am happy to say I am 
not given to punning during waking life, though I 
had a fit of it once. It strikes me that punning, 
consisting as it does essentially of overlooking 
sense and attending to sound, is just such a debased 
kind of intellectual activity as one might look for 
in sleep. 
* See Radestock, op. cit., ch it. ; l 
rJ*c Traumes mii dtm Wahnsinn. 52 
ILLUSIONS: A PSYCHOLOGICAL STUDY. 
pation ot dream-hallucination in the presom- 
nial condition, so there is the survival of it in 
the postsomnial condition. As I have ob- 
served, dreams sometimes leave behind them, 
for an appreciable interval after waking, a 
vivid after-impression, and in some cases 
even the semblance of a sense-perception. 
If one reflects how many ghosts and other 
miraculous apparitions are seen at night, 
and when the mind is in a more or less som- 
nolent condition, the idea is forcibly suggest- 
ed that a good proportion of these visions 
are the dibris of dreams. In some cases, 
indeed, as that of Spinoza, already referred to, 
the hallucination (in Spinoza’s case that of “ a 
scurvy black Brazilian ”) is recognized by 
the subject himself as a dream-image.* j 
am indebted to Mr. W. H. Pollock for a 
fact which curiously illustrates the position 
here adopted. A lady was staying at a 
country house. During the night and imme- 
diately on waking up she had an apparition 
of a strange-looking man in mediaeval cos- 
tume, a figure by no means agreeable, and 
which seemed altogether unfamiliar to her. 
The next morning, on rising, she recognized 
the original of her hallucinatory image in a 
portrait hanging on the wall of her bedroom, 
which must have impressed itself on her 
brain before the occurrence of the appari- 
tion, though she had not attended to it. 
Oddly enough, she now learnt for the first 
time that the house at which she was staying 
had the reputation of being haunted, and by 
the very same somewhat repulsive-looking 
mediaeval personage that had troubled her 
inter-somnolent moments. The case seems 
to me to be typical with respect to the gen- 
esis of ghosts, and of the reputation of 
haunted houses. 
* For Spinoza’s experience, given in his own 
words, see Mr. F. Pollock’s Spinoza, p. 57 ; cf. 
what Wundt says on his experience, Physiologische 
Psychologies p> 648, footnote a. CATALOGUE 
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its History and Present Development. 
FREDRIK BJORNSTROM, M. D., 
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Medical Counselor. 
Authorized Translation from the Second Swedish Edition. 
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PRESS NOTICES. 
The learned Swedish physician, Bjornstrom.—Churchman. 
It is a strange and mysterious subject this hypnotism.— The Sun. 
Perhaps as concise as any work we have.—S. California Practitioner. 
We have found this book exceedingly interesting.—California Homcepath, 
A concifee, thorough, and scientific examination of a little-understood subject.—Episcopal 
Recorder. 
Few of the new books have more Interest for scientist and layman alike.—Sunday Tunes 
(Boston). 
The study of hypnotism is in fashion again. It is a fascinating and dangerous study.— 
Toledo Bee. 
It is well written, being concise, which is a difficult point to master in all translations.— 
Medical Bulletin (Philadelphia). 
The subject will be fascinating to many, and it receives a cautious yet sympathetic 
treatment in this book.—Evangelist. 
One of the most timely works of the hour. No physician who would keep up with the 
times can afford to be without this work.—Quarterly Journal of Inebriety„ 
Its aim has been to give all the information that may be said under the present state of 
our knowledge. Every physician should read this volume.—Ameri an Medical Journal (St. 
Louis). 
Is a contribution of decided value to a much-discussed and but little-analyzed subject by 
an eminent Swedish alienist known to American students of European psychiatry.—Medical 
Standard (Chicago). 
This is a highly interesting and instructive book. Hypnotism is on the onward march 
to the front as a scientific subject for serious thought and investigation.—The Medical Free 
Press (Indianapolis). 
Many of the mysteries of mesmerism, and all that class of manifestation, are here 
treated at length, and explained as far as they can be with our present knowledge of psy- 
chology.—New York Journal of Commerce. 
The marvels of hypnotic phenomena increase with investigation. Dr. BjornstrSm, in 
this clear and well-written essay, has given about all that modern science has been able to 
develop of these phenomena.—Medical Visitor (Chicago). 
It has become a matter of scientific research, and engages the attention of some of the 
foremost men of the day, like Charcot, of Paris. It is interesting reading, outside of any 
usefulness, and may take the place of a novel on the office table.—Eclectic Medical Journal 
(Cincinnati). 
This interesting book contains a scholarly account of the history, development, and 
scientific aspect of hypnotism. As a whole, the book is of great interest and very instruc- 
tive. It is worthy of careful perusal by all physicians, and contains nothing unfit to be read 
by the laity.—Medical and Surgical Reporter (Philadelphia). 
To define the real nature of hypnotism is as difficult as to explain the philosophy of toxic 
or therapeutic action of medicine—more so, indeed. None the less, however, doe« it 
behoove the practitioner to understand what it does, even if he cannot tell just wha* i* is, «or 
how it operates. Dr. Bjdrnstrom’s book aims to give a general review of the entire aubjee*. 
—Medical Record, This is an able, thoughtful, and scientific examination of a subject of far more serious 
Importance than has generally been conceded to it. Dr. Bjornstrom takes the true and 
serious view of the subject, and discusses it not only with ample learning, but in a scientific 
spirit, showing its nature, its origin, its power for good or evil, and its dangers.—Illustrated 
Christian Weekly. 
One of the most interesting works that have yet appeared on that intensely interesting, 
though almost invariably dryly-written subject. It includes accuracy, as well as the gift of 
entertaining description and discussion. It is not too much to add that for any one who 
wishes to become en rapport with present opinion respecting hypnotism, its phases, nature, 
and effects, nothing so good has yet appeared upon the subject in the English language.— 
Public Opinion. 
The work is purely expository in character, and offers about as convenient an introduc- 
tion to the subject as we have in English. The topics are well selected, the points clearly 
stated, and the whole fairly represents the present status of investigation upon this vexed 
phenomenon. A general historical introduction is followed by a chapter defining the ordin- 
ary hypnotic condition, according to various authorities. The method of hypnotizing and 
the stages of hypnotism are next interestingly discussed.—Science. 
The discoveries of scientific explorers in this attractive but perilous field have nowhere 
else been presented in a more condensed yet comprehensive, lucid, and effective form than 
in this admirable and highly interesting work. The author, instead of wearying the reader 
with prolix detailing of his personal work and theories, has collated and arranged, system- 
atically and well, the facts clearly established by the best authorities, enabling a clear under- 
standing of the extent and limitation of Western knowledge in this department of science.— 
The Path. 
Hypnotism is of late claiming much attention among medical men. This book treats, in a 
thorough manner, of its discovery, growth, and present status. It gives the physical and 
psychical effects of the hypnotic sleep, and expresses the opinion that, in so far as it affects 
the imagination, it may be used as a remedial agent, and also in soothing and invigorating 
the patient. It is also claimed that by hypnotism negligent and lazy and also mentally weak 
students may be aroused to successful efforts. This is one of the most interesting numbers 
of the “ Humboldt Library.”—Nassau Literary Gazette (Princeton). 
The recent revival of hypnotism compels every medical man to give some thought to 
the matter, and to ask the question whether the therapeutic effects are not outweighed by 
the physical effects of hypnotism, the diminished individuality of the patient, and the great 
scope which such practices afford for the perpetration of crime. All these questions are 
very fairly discussed in the work before us. We recommend a careful perusal of the above 
work to all our professional brethren, that they may realize, to some extent, the gravity of a 
question that will soon be propounded to them.—Occidental Medical Times (San Francisco). 
One of the most interesting and remarkable books we have read for many a day, con- 
taining revelations regarding this new department of science more startling and extraordinary 
than anything to be found in the pages of romance. It is not at all a work of the imagination, 
or by some bold and reckless speculative genius. Its author is Frederik Bjornstrdm, M.D., 
Head Physician of the Stockholm Hospital, and a Royal Swedish Medical Councillor. This 
eminent scientific writer has devoted his talents to an investigation of a subject which is 
regarded by the generality of persons as unworthy of serious attention. The present 
volume is an exhaustive treatise on the subject, embodying all the results of the ablest ex- 
perimenters and investigators, and leaving nothing to be desired. It is written in a clear 
and captivating style, and, the narratives and experiments are of the most extraordinary 
character, and were they not attested by scientists, would be regarded as passing the 
bounds of belief.—Evening Mercury (St. John’s, Newfoundland). 
Mesmerism and animal magnetism are terms that have been used to cover much that is 
absurdly erroneous, and it is time that they should be rescued from the misuse they have 
suffered at the hands of ignorant quacks and charlatans, and that the many interesting and 
remarkable phenomena relating to the subject should be seriously and thoroughly investi- 
gated. Few books on the subject are of a truly scientific nature, and it is therefore with 
pleasure that we record the appearance of such a thorough and satisfactory work as “ Hyp- 
notism : Its History and Present Development,” by Frederik Bjornstrom, M.D. The author 
has spent many years in research, and brings to bear upon the subject an experienced mind, 
scientifically trained, cautious in judgment, and guided by strong common sense. These 
latter traits are especially valuable in a discussion that involves matters that have too 
frequently been subjected to the wildest and most extravagant speculation. The book is a 
complete statement of the truly scientific view of the subject,— The Book Buyer. 
FOR SALE BY YOUR NEWSDEALER. A Remarkable Book.—Edward Bellamy. 
THE 
Kingdom of the Unselfish; 
OR, 
EMPIRE OF THE WISE. 
By JOHN LORD PECK. 
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existence will find much inspiration in 4 The Kingdom of the Unselfish.”’—The Arena. 
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