Illusions

Illusions

The Project Gutenberg EBook of Illusions, by James Sully This eBook
is for the use of anyone anywhere at no cost and with almost no
restrictions whatsoever. You may copy it, give it away or re-use it
under the terms of the Project Gutenberg License included with this
eBook or online at www.gutenberg.org
Title: Illusions A Psychological Study
Author: James Sully
Release Date: February 21, 2006 [EBook #17815]
Language: English
Character set encoding: ISO-8859-1
*** START OF THIS PROJECT GUTENBERG EBOOK
ILLUSIONS ***

Produced by Thierry Alberto, Janet Blenkinship and the Online
Distributed Proofreaders Europe at http://dp.rastko.net

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