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~ILLUSIONS~
_A PSYCHOLOGICAL STUDY_
BY
JAMES SULLY
AUTHOR OF "SENSATION AND INTUITION," "PESSIMISM," ETC.
THIRD EDITION
LONDON
KEGAN PAUL, TRENCH & CO., 1, PATERNOSTER SQUARE
1887
(_The rights of translation and of reproduction are reserved_)
~THE INTERNATIONAL SCIENTIFIC SERIES.~
VOL. XXXIV.
PREFACE.
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
illusions, and resembling the former in their structure and mode of
origin. I have throughout endeavoured 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 considerable extent, rewritten.
J. S.
_Hampstead, April, 1881._
CONTENTS.
CHAPTER I.
THE STUDY OF ILLUSION.
Vulgar idea of Illusion, 1, 2; Psychological treatment of subject,
3, 4; definition of Illusion, 4-7; Philosophic extension of idea,
7, 8.
CHAPTER II.
THE CLASSIFICATION OF ILLUSIONS.
Popular and Scientific conceptions of Mind, 9, 10; Illusion and
Hallucination, 11-13; varieties of Immediate Knowledge, 13-16; four-fold
division of Illusions, 16-18.
CHAPTER III.
ILLUSIONS OF PERCEPTION: GENERAL.
_Psychology of Perception_:--The Psychological analysis of Perception,
19, 20; Sensation and its discrimination, etc., 20, 21; interpretation
of Sensation, 22, 23; construction of material object, 23, 24;
recognition of object, specific and individual, 24-27; Preperception
and Perception, 27-31; Physiological conditions of Perception, 31-33;
Visual and other Sense-perception, 33, 34.
_Illusions of Perception_:--Illusion of Perception defined, 35-38;
sources of Sense-illusion, 38-40: (a) confusion of
Sense-impression, 40-44; (b) misinterpretation of Sense-impression, 44;
Passive and Active misinterpretation, 44-46; Passive Illusions as
organically and extra-organically conditioned, 46-49.
CHAPTER IV.
ILLUSIONS OF PERCEPTION--_continued_.
A. _Passive Illusions (a) as determined by the Organism._
_Results of Limits of Sensibility_:--Relation of quantity of Sensation to
that of Stimulus, 50-52; coalescence of simultaneous Sensations,
52-55; after-effect of Stimulation, 55, 56; effects of prolonged
Stimulation, 56-58; Specific Energy of Nerves, 58, 59; localization
of Sensation, 59-62; Subjective Sensations, 62-64.
_Results of Variation of Sensibility_:--Rise and fall of Sensibility,
64-67; Paræsesthesia, 67, 68; _rationale_ of organically conditioned
Illusions, 68, 69.
CHAPTER V.
ILLUSIONS OF PERCEPTION--_continued_.
A. _Passive Illusions (b) as determined by the Environment._
_Exceptional Relation of Stimulus to Organ_:--Displacement of organ,
etc., 70-72.
_Exceptional Arrangement of Circumstances in the Environment_:--
Misinterpretation of the direction and movement of objects, 72-75;
misperception of Distance, 75, 76; Illusions of depth, relief, and
solidity in Art, 77-81; Illusions connected with the perception of
objects through transparent coloured media, 82-84; visual transformation
of concave into convex form, 84-86; false recognition of
objects, 86, 87; inattention to Sense-impression in Recognition,
87-91; suggestion taking the direction of familiar recurring experiences,
91, 92.
CHAPTER VI.
ILLUSIONS OF PERCEPTION--_continued_.
B. _Active Illusions._
Preperception and Illusion, 93-95.
_Voluntary Preperception_:--Choice of interpretation in the case of
visible movement, 95, 96; and in the case of flat projections of form,
96-98; capricious interpretation of obscure impressions, 99, 100.
_Involuntary Preperception_:--Effects of permanent Predisposition,
101, 102; effects of partial temporary Preadjustment, 102-105;
complete Pro-adjustment or Expectation, 106-109; subordination of
Sense-impression to Preperception, 109-111; transition from Illusion
to Hallucination, 111, 112; rudimentary Hallucinations, 112-114;
developed Hallucinations, 114-116; Hallucination in normal life,
116, 117; Hallucinations of insanity, 118-120; gradual development
of Sense-illusions, and continuity of normal and abnormal life; 120-123;
Sanity and Insanity distinguished, 123-126.
CHAPTER VII.
DREAMS.
Mystery of sleep, 127, 128; theories of Dreams, 128, 129; scientific
explanation of Dreams, 129, 130.
_Sleep and Dreaming_:--Condition of organism during sleep, 131, 132;
Are the nervous centres ever wholly inactive during sleep? 132-134;
nature of cerebral activity involved in Dreams, 134-136; psychical
conditions of Dreams, 136-138.
_The Dream as Illusion_:--External Sense-impressions as excitants of
Dream-images, 139-143; internal "subjective" stimuli in the sense-organs,
143-145; organic sensations, 145-147; how sensations are
exaggerated in Dream-interpretation, 147-151.
_The Dream as Hallucination_:--Results of direct central stimulation
151-153; indirect central stimulation and association, 153-155.
_The Form and Structure of Dreams_:--The incoherence of Dreams explained,
156-161; coherence and unity of Dream as effected (a) by
coalescence and transformation of images, 161-163; (b) by aground-tone
of feeling, 164-168; (c) by the play of associative dispositions,
168-172; (d) by the activities of selective attention stimulated by
the rational impulse to connect and to arrange, 172-176; examples
of Dreams, 176-179; limits of intelligence and rational activity in
Dreams, 180-182; Dreaming and mental disease, 182, 183; After-dreams
and Apparitions, 183-185.
NOTE.--The Hypnotic Condition, 185-188.
CHAPTER VIII.
ILLUSIONS OF INTROSPECTION.
Illusions of Introspection defined, 189-192; question of the possibility
of illusory Introspection, 192-194; incomplete grasp of internal
feelings as such, 194-196; misobservation of internal feelings: Passive
Illusions, 196-199; Active Illusions, 199-202; malobservation of
subjective states, 202-205; Illusory Introspection in psychology and
philosophy, 205-208; value of the Introspective method, 208-211.
CHAPTER IX.
OTHER QUASI-PRESENTATIVE ILLUSIONS: ERRORS OF INSIGHT.
Emotion and Perception, 212; Æsthetic Intuition, 213; Subjective
Impressions of beauty misinterpreted, 213-216; analogous Emotional
Intuitions, 216, 217; Insight, its nature, 217-220; Passive Illusions
of Insight, 220-222; Active Illusions of Insight: projection of
individual feelings, 222-224; the poetic transformation of nature,
224-226; special predispositions as falsifying Insight, 226-228;
value of faculty of Insight, 228-230.
CHAPTER X.
ILLUSIONS OF MEMORY.
Vulgar confidence in Memory, 231-233; definition of Memory, 233-235;
Psychology of Memory, 235-237; Physiology of Memory, 237, 238;
Memory as localization in the past, 238-241; Illusions of Memory
classified, 241-245.
(1) _Illusions of Time-Perspective_:--
(a) Definite Localization of events: constant errors in retrospective
estimate of time, 245-249; varying errors: estimate of duration
during a period, 249-251; variations in retrospective estimate of
duration, 251-256.
(b) Indefinite Localization: effect of vividness of mnemonic image
on the apparent distance of events, 256-258; isolated public events,
258, 259; active element in errors of Localization, 259-261.
(2) _Distortions of Memory_:--Transformation of past through
forgetfulness, 261-264; confusion of distinct recollections, 264-266;
Active Illusion: influence of present imaginative activity, 266-269;
exaggeration in recollections of remote experiences, 269, 270; action of
present feeling in transforming past, 270, 271.
(3) _Hallucinations of Memory_:--Their nature, 271-273; past dreams taken
for external experiences, 273-277; past waking imagination taken
for external reality, 277-280; recollection of prenatal ancestral
experience, 280, 281; filling up gaps in recollection, 281-283.
_Illusions connected with, Personal Identity_:--Illusions of Memory and
Sense of identity, 283, 284; idea of permanent self, how built up,
285-287; disturbances of sense of identity, 287-290; fallibility and
trustworthiness of Memory, 290-292.
NOTE.--Momentary Illusions of Self-consciousness, 293.
CHAPTER XI.
ILLUSIONS OF BELIEF.
Belief as Immediate or Intuitive, 294-296; simple and compound
Belief, 296.
A. _Simple Illusory Belief_:--
(1) Expectation: its nature, 297, 298; Is Expectation ever intuitive?
298; Expectation and Inference from the past, 299-301; Expectation
of new kinds of experience, 301, 302; Permanent Expectations
of remote events, 302; misrepresentation of future duration,
302-305; Imaginative transformation of future, 305-307.
(2) Quasi-Expectations: anticipation of extra-personal experiences,
307, 308; Retrospective Beliefs, 308-312.
B. _Compound Illusory Belief_:--
(1) Representations of permanent things: their structure, 312; our
representations of others as illusory, 312-315; our representation
of ourselves as illusory, 315; Illusion of self-esteem, 316-318;
genesis of illusory opinion of self, 318-322; Illusion in our
representations of classes of things, 322, 323; and in our views
of the world as a whole, 323, 324; tendency of belief towards
divergence, 325; and towards convergence, 326, 327.
CHAPTER XII.
RESULTS.
Range of Illusion, 328-330; nature and causes of Illusion in general,
331-334; Illusion identical with Fallacy, 334; Illusion as abnormal,
336, 337; question of common error, 337-339; evolutionist's conception
of error as maladaptation, 339-344; common intuitions
tested only by philosophy, 344; assumptions of science respecting
external reality, etc., 344-346; philosophic investigation of these
assumptions, 346-348; connection between scientific and philosophic
consideration of Illusion, 348-350; correction of Illusion and its
implications, 351, 352; Fundamental Intuitions and modern psychology,
352; psychology as positive science and as philosophy, 353-355;
points of resemblance between acknowledged Illusions and Fundamental
Intuitions, 355, 356; question of origin, and question of
validity, 356, 357; attitude of scientific mind towards philosophic
scepticism, 357-360; Persistent Intuitions must be taken as true,
360, 361.
~ILLUSIONS.~
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
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 of mediæval
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 something essentially abnormal and
allied to insanity. 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 procedure has in the main
conformed to this distinction of common sense. The phenomena of illusion
have ordinarily been investigated 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 that 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 diametrically 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 condition of mortals. This idea has found expression, not only
in the cynical exclamation of the misanthropist that most men are fools,
but also in the cry of despair that sometimes 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 mankind, we must recognize the fact that most men are
sometimes liable to illusion. Hardly 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
example: 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 imaginative 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
enlightenment 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 further, and say that in the analysis and
explanation 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 naturally 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 recognize. The psychologist has a different interest in the
subject, being specially concerned to understand the mental antecedents
of illusion and its relation to accurate perception and belief. It is
pretty evident, indeed, 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 of 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 abnormal
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 border-land 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
limitation, 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 under 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 notions of
ourselves are, for the most part, obtained apart from any process of
inference. The view which a man takes of his own character 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 commonly 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
certainty.
Taking this view of illusion, we may provisionally define it as any
species of error which counterfeits the form of immediate, self-evident,
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 inferences. If
for the present we roughly divide all our knowledge into the two regions
of primary or intuitive, and secondary or inferential knowledge, we see
that illusion is false or spurious knowledge of the first kind, fallacy
false or spurious knowledge of the second kind. At the same time, it is
to be remembered 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, according as we are thinking of its
original mode of production or of the form which it finally assumes; 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 respecting
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 philosophers have still further
extended the idea of illusion by seeking to bring under it beliefs which
the common sense of mankind has always adopted and never begun to
suspect. Thus, according to the idealist, the popular notion (the
existence of which Berkeley, however, 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 yet assume 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 assumed as something above all question.
And a rough and provisional, though for our purpose sufficiently
accurate, demarcation of the regions of the real and the 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 contradiction to this. For our present
purpose the real is that which is true for all. Thus, though physical
science may tell us that there is nothing corresponding to our
sensations of colour in the world of matter and motion which it
conceives as surrounding us; yet, inasmuch as to all men endowed with
the normal colour-sense the same material objects appear to have the
same colour, 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
consensus. From this point of view illusion is seen to arise through
some exceptional feature in the situation or condition of the
individual, 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 concern us here. For
our present purpose, which is the determination and explanation of
illusion as popularly understood, it is sufficient that there is this
general consensus of belief, and this may provisionally be regarded as
at least practically true.