Illusions A Psychological Study   By: James Sully (1842-1923)

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.