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- Herausgeber: Booksell-Verlag
- Kategorie: Geisteswissenschaft
- Sprache: Englisch
In "Illusions: A Psychological Study," James Sully delves into the intricacies of human perception and experience, offering a profound exploration of the illusory nature of reality. Using a blend of empirical investigation and philosophical inquiry, Sully employs a clear and engaging literary style to dissect various forms of illusions'—visual, auditory, and cognitive'—highlighting how these phenomena shape our understanding of truth. The book situates itself within the context of late 19th-century psychology, a time when the scientific study of consciousness was burgeoning, and reflects prevailing themes in the exploration of mental phenomena. James Sully, a prominent figure in psychology and philosophy, was deeply influenced by the advancements in psychological theory occurring during his time. His own academic journey'—moving through disciplines of philosophy and psychology'—provided him with the tools to thoughtfully examine the relationship between perception and reality. Sully's commitment to science and introspection enabled him to appreciate how personal and societal factors contribute to the allure of illusions. This book is highly recommended for readers interested in psychology, philosophy, and the arts, as it not only challenges preconceived notions of reality but also invites readers to engage with their own perceptual experiences. Sully's insightful analysis serves as a valuable resource for anyone seeking to understand the complexities of human perception. In this enriched edition, we have carefully created added value for your reading experience: - A succinct Introduction situates the work's timeless appeal and themes. - The Synopsis outlines the central plot, highlighting key developments without spoiling critical twists. - A detailed Historical Context immerses you in the era's events and influences that shaped the writing. - A thorough Analysis dissects symbols, motifs, and character arcs to unearth underlying meanings. - Reflection questions prompt you to engage personally with the work's messages, connecting them to modern life. - Hand‐picked Memorable Quotes shine a spotlight on moments of literary brilliance. - Interactive footnotes clarify unusual references, historical allusions, and archaic phrases for an effortless, more informed read.
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Veröffentlichungsjahr: 2019
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Illusions: A Psychological Study
Table of Contents
Introduction
Illusions reveal how the mind constructs reality—and how those constructions can fail us. In Illusions: A Psychological Study, James Sully investigates the ways perception and thought can be led astray, not as curiosities but as windows into the mind’s ordinary workings. He treats errors as systematic, meaningful, and instructive, showing that misperception often follows rules that reveal underlying mental processes. The result is a careful, methodical inquiry that treats illusion as a legitimate object of scientific study. Readers encounter a work intent on mapping the boundary between appearance and fact, and on clarifying how that boundary is drawn within us.
This is a work of psychological nonfiction by the British psychologist and philosopher James Sully, first published in 1881 during the late Victorian emergence of scientific psychology. Situated at a moment when experimental methods and physiological insights were reshaping the study of mind, the book blends philosophical reflection with empirical sensibility. Its pages engage the era’s growing interest in perception, attention, and error. Rather than a clinical casebook or a manual of tricks, it is a broad, scholarly treatment of illusion as a pervasive human phenomenon. The intellectual setting is the transition from speculative psychology to a more observational, systematic discipline.
The premise is straightforward and fertile: to understand the mind, study its mistakes. Sully surveys illusions arising in ordinary perception and in higher mental activity, showing how context, habit, expectation, and interpretation shape what we take to be real. The reading experience is reflective and analytic, favoring clear exposition and careful distinctions. The voice is measured and instructive, inviting readers to examine familiar experiences with new rigor. Expect patient classification, illustrative examples, and an emphasis on explanation over sensation. The mood is curious rather than sensational, committed to demystifying error without dismissing the wonder—and occasional danger—of being misled.
Key themes include the fallibility of the senses, the constructive nature of perception, and the influence of attention and prior belief on what we seem to see or know. Sully’s analysis highlights how normal cognitive operations can produce systematic distortions, blurring any simple divide between everyday seeing and extraordinary misperception. He underscores the roles of context and contrast, the ways familiarity can stabilize or misdirect judgment, and the limits of introspection when examining one’s own mental states. Throughout, the study suggests that illusions are not merely accidents but regular outcomes of efficient processes, which ordinarily serve us well yet can be pushed into error.
Historically, the book stands at a crossroads where psychology draws from physiology, philosophy, and emerging experimental practice. Sully writes with awareness of contemporary scientific debates, organizing a diverse literature of observation into a coherent account of how illusions arise and persist. He favors explanation grounded in lawful tendencies rather than in isolated marvels, which gives the work a durable clarity. The method is comparative and synthetic: relate varieties of illusion, note recurring conditions, and infer the mental operations at work. Readers today will recognize the outlines of questions that later became central to perception research and cognitive psychology.
For modern readers, the value lies in its disciplined skepticism and its practical illumination of everyday life. The book offers a framework for interrogating testimony, visual impressions, and confident but mistaken judgments—issues that resonate amid abundant information and persuasive media. It encourages habits of careful observation and self-scrutiny without cynicism, showing how error can be anticipated and, at times, corrected. The prose rewards patience: its pace reflects a commitment to precision and to drawing distinctions that matter. Rather than presenting a catalog of curiosities, the text builds a conceptual toolkit for recognizing patterns behind the bewildering variety of misleading appearances.
Approached as a classic of late nineteenth-century psychology, Illusions: A Psychological Study remains a lucid guide to the mind’s tendencies under uncertainty. Sully’s restraint and clarity make the work accessible, while its analytic structure gives it lasting usefulness. Readers will find not just descriptions of striking effects but a disciplined inquiry into their causes and conditions. The book ultimately models intellectual humility: trust perception, but test it; value judgment, but examine its supports. In doing so, it equips us to navigate a world where appearances are inevitable, interpretations are necessary, and the line between the two demands continual, thoughtful attention.
Synopsis
James Sully’s Illusions: A Psychological Study sets out to examine systematic errors in human experience, distinguishing carefully between illusions—misinterpretations of real sensory input—and hallucinations, which arise without corresponding external stimuli. He proposes a psychological approach grounded in physiology and introspection, aiming to show how normal mental processes yield persistent inaccuracies. After outlining his method and historical context, Sully classifies illusions by source: perceptual (linked to the senses), representative (involving memory and imagination), and intellectual (arising from judgment and belief). He frames the inquiry as a way to map the constructive operations of mind, tracing how lawful mental tendencies can mislead perception and thought.
Early chapters identify general conditions that predispose the mind to error. Sully stresses the role of attention, expectation, and habit in shaping interpretations of ambiguous input, emphasizing that perception depends on learned cues and prior experience. He describes how contrast and assimilation alter impressions, how brief or intense stimuli can bias interpretation, and how bodily states modulate receptivity. The nervous system’s economy—seeking swift, coherent meanings—produces shortcuts that sometimes overshoot accuracy. These broad principles, he argues, govern illusions across modalities. With these foundations, Sully proceeds from simple sensory misreadings to more intricate, compounded errors in memory, judgment, and social belief.
Sully devotes substantial attention to vision, cataloging illusions of size, distance, direction, and form. He explains how perspective, foreshortening, and habitual cues about light and shadow foster convincing yet misleading constructions of depth and contour. Contrast effects alter perceived brightness and color, while context and framing shift apparent lengths, angles, and curvature. The coordination of eye movements and binocular disparity, usually a benefit, can generate errors in judging relative placement or motion. He illustrates how the visual system completes incomplete figures, stabilizes the world despite eye motion, and infers shape from scant evidence—processes efficient for everyday use yet occasionally at odds with physical measurements.
Turning to other senses, Sully surveys illusions of hearing, touch, taste, and smell. In audition, mislocalization arises from echoes and conflicting cues, while concurrent sounds may fuse or produce illusory patterns. The ventriloquial misattribution of voice to a visible source exemplifies cross-modal influence. Touch and temperature judgments are swayed by prior contact and contrast, and apparent weight varies with expectations shaped by size and material. Taste and smell blend in ways that obscure each sense’s contribution, leading to misidentification under altered conditions. He notes how temporal and numerical perceptions—beats, rhythms, and counts—are likewise susceptible to grouping and emphasis effects.
From elementary errors, Sully progresses to composite illusions created by learned associations and cultural arts. Painting and sculpture elicit depth, texture, and motion through selective cues, exploiting the mind’s readiness to infer solidity from shading, perspective, and outline. The stage crafts convincing realities using lighting, scale, and framing; conjuring arts rely on directing attention and expectation to mask causal steps. Everyday displays and optical devices further demonstrate how stable cues can override conflicting details. These cases underscore Sully’s thesis that perception is inferential: a constructive process that integrates fragmentary signals with organized knowledge, sometimes achieving striking verisimilitude at the cost of literal accuracy.
Sully then contrasts ordinary illusions with hallucinations and dream experiences, examining conditions under which images gain perceptual force without appropriate stimuli. In dreams, memory fragments combine with faint sensations to form coherent scenarios, with weakened critical control allowing improbable unions. Transitional states amplify after-images, lingering impressions, and suggestive associations. In delirium and certain mental disorders, heightened imagery or impaired judgment yields persistent misinterpretations or unfounded perceptions. By differentiating illusion from hallucination in origin and controllability, Sully situates them on a continuum, showing how normal mechanisms—attention, suggestion, and expectation—can, with altered vigilance or emotion, produce experiences that approximate pathology.
Beyond the senses, Sully analyzes representative and introspective illusions—errors of memory, belief, and self-knowledge. He describes false recognitions, confusions of source, and retrospective distortions imposed by current attitudes. Testimony, he notes, is shaped by selective attention and narrative coherence, producing sincere yet inaccurate reports. Anticipation and desire color both recollection and ongoing experience, biasing judgments of time, causation, and probability. Introspective errors arise when people infer motives or feelings from theories rather than observation, or overlook unconscious determinants. These phenomena extend the same constructive tendencies found in perception, showing how the mind organizes evidence to preserve order, sometimes at truth’s expense.
Sully further discusses intellectual and social illusions, tracing how language, custom, and authority stabilize shared misapprehensions. He considers the role of naming in hardening vague distinctions, the influence of tradition and prestige in guiding assent, and the ease with which generalizations outrun their evidence. Children’s credulity and imaginative play illustrate developmental pathways through which conventions become taken as realities. Superstitions and popular errors persist, he suggests, through reinforcement, emotional utility, and group transmission. Education and scientific method provide correctives by cultivating measurement, controlled comparison, and critical doubt, thereby checking associative leaps and clarifying where inference properly extends.
The study concludes by emphasizing the dual lesson of illusions: they expose vulnerabilities in human cognition while also revealing the adaptive, constructive power of mind. Sully argues that systematic investigation—linking physiology, experiment, and reflective analysis—can map these errors, distinguish their sources, and propose remedies. Training attention, refining observation, and testing beliefs against stable standards help reduce mistakes without denying the efficiencies that usually serve practical life. Art and science alike harness the same mechanisms that produce illusions, turning them toward insight or aesthetic effect. The book’s central message is that understanding error illuminates the very processes that underwrite everyday knowledge.
Historical Context
James Sully’s Illusions: A Psychological Study (published in London in 1881) emerges from late Victorian Britain, a period marked by industrial urbanization, expanding print culture, and the institutional consolidation of science. Its intellectual geography spans London’s lecture halls and journals (notably Mind, founded in 1876) and the German university laboratories that led the new experimental psychology. Sully, an English philosopher-psychologist trained amid British empiricism and receptive to German research, wrote for a public increasingly educated by the 1870 Elementary Education Act. The book’s setting is thus not a fictional milieu but the scientific and civic spaces of the 1870s–1880s, where debates over perception, evidence, and authority animated universities, courts, theaters, and salons.
The Darwinian revolution reshaped explanatory ideals in Britain after Charles Darwin’s On the Origin of Species (1859) and The Descent of Man (1871). Public controversies, including the 1860 Oxford debate between T. H. Huxley and Bishop Samuel Wilberforce and John Tyndall’s Belfast Address (1874), normalized naturalistic accounts of life and mind. The X Club (founded 1864) advanced scientific naturalism in London institutions. Within this climate, Sully situated illusions as lawful, adaptive by-products of sensory mechanisms shaped by evolution, not as signs of supernatural influence. His analyses echo Darwin-era comparative thinking, treating perceptual error as a feature to be explained by history, physiology, and environment rather than metaphysical speculation.
The institutional birth of experimental psychology profoundly framed Sully’s project. Gustav Fechner’s Elemente der Psychophysik (Leipzig, 1860) quantified sensation via just-noticeable differences and logarithmic laws; F. C. Donders in Utrecht (1868) introduced mental chronometry; and Wilhelm Wundt founded the first psychology laboratory at Leipzig in 1879, using chronoscopes and kymographs to time perception and attention. Hermann von Helmholtz’s measurements of nerve conduction (c. 1849–1852) and reaction time solidified a physiological basis for mental processes. British readers accessed these findings through translation, lectures, and journals in the 1870s. Sully’s 1881 synthesis relayed continental experimental results to an English audience, recasting illusions as measurable, reproducible phenomena anchored in sensory thresholds and cognitive timing.
Nineteenth-century advances in physiological optics furnished exemplary cases of illusion that Sully cataloged and interpreted. Helmholtz’s Handbuch der physiologischen Optik (1856–1866) and the Young–Helmholtz trichromatic theory helped explain color and contrast effects; Ewald Hering (1861; later 1878) advanced opponent-color processes and motion illusions. Classic geometric illusions—the Zöllner illusion (described in 1860), the Poggendorff illusion (reported in 1860), and Hering’s radial lines illusion (1861)—demonstrated systematic misperception of parallelism, alignment, and size. Devices such as Wheatstone’s stereoscope (King’s College London, 1838) and Plateau’s spinning disks made binocular disparity and flicker salient. In popular venues, Pepper’s Ghost (Royal Polytechnic Institution, London, 1862) dramatized perceptual susceptibility. Sully used these cases to show how sensory apparatus and inference rules generate predictable errors.
Shifts in psychiatry and neurology provided a clinical backdrop for distinguishing illusion from hallucination. The Lunacy Act (1845) expanded county asylums in England and Wales, and Henry Maudsley’s The Physiology and Pathology of Mind (London, 1867; rev. 1879) integrated medical views of disordered perception. On the Continent, Jean-Martin Charcot’s public lessons at the Salpêtrière in Paris (c. 1878–1893) analyzed hysteria, anesthesia, and hypnosis; the Nancy School (Liébeault, Bernheim) emphasized suggestibility in the 1880s. These investigations tied error to nervous function and attention. Sully drew on clinical reports to argue for a continuum between normal illusions and pathological hallucinations, clarifying mechanisms—sensory defect, expectancy, association—rather than invoking moral failing or demonic influence.
The transatlantic spiritualist movement challenged Victorian standards of evidence, provoking legal and scientific responses. After the Fox sisters’ 1848 séances in New York, mediums toured Britain; Daniel D. Home performed in London in the 1850s–1860s. The 1876 London trial of Henry Slade for fraudulent mediumship, pursued by biologist E. Ray Lankester, dramatized courtroom scrutiny of testimony and perception. The Society for Psychical Research (London, 1882), led by Henry Sidgwick, Edmund Gurney, and F. W. H. Myers, sought systematic inquiry into apparitions and telepathy. Sully’s analyses of error, suggestion, and witness fallibility supplied naturalistic interpretations for phenomena claimed by spiritualists, aligning with efforts to separate illusion, deception, and sincere misperception from the supernatural.
Expanding mass education and public science amplified both demonstrations and misreadings of perceptual phenomena. The Elementary Education Act (1870) raised literacy, enlarging readerships for periodicals such as Mind (from 1876) and for popular lectures at the Royal Institution and the Royal Polytechnic. Exhibitions—from the Great Exhibition at the Crystal Palace (1851) to the 1862 International Exhibition—featured optical devices, magic lanterns, and spectacular stage effects that capitalized on persistence of vision and depth cues. Francis Galton’s Nature inquiries into mental imagery (1880) and later anthropometric measurements (South Kensington, 1884) encouraged quantifying individual differences. Sully wrote into this milieu, using public, replicable displays of illusion to educate readers about perception’s constructive, error-prone character.
Illusions functions as a social and political critique by challenging the period’s overconfidence in untrained observation, eyewitness testimony, and authority. By demonstrating lawful sources of error—expectation, attention, sensory limits—it calls for procedural safeguards in courts, laboratories, and the press. The book implicitly contests the commercial exploitation of credulity in spiritualist markets and theatrical pseudo-science, promoting a civic ideal of methodological skepticism accessible to the educated public. It also questions punitive or moralistic interpretations of disordered perception, favoring medical and environmental explanations over stigma in asylum practice. In late Victorian disputes over science, religion, and evidence, Sully’s analysis advances a secular ethic of responsibility in seeing and believing.
Illusions: A Psychological Study
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.
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[2] plumes itself on having got at the bottom of mediæval visions and church miracles[3], 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[1], 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.[1q] 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.
CHAPTER II.
THE CLASSIFICATION OF ILLUSIONS.
If illusion is the simulation of immediate knowledge, the most obvious mode of classifying illusions would appear to be according 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 unreasoned or uninferred knowledge. Of these the two best known are perception and memory. When I see an object before me, or when I recall an event in my past experience, I 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 representative process, namely, that of reproduction, or on the evidence of memory. In the one case the object of cognition is present 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 distinctions. Just as the zoologist sometimes groups together varieties of animals which the unscientific eye would never think of connecting, so the psychologist may analyze mental operations which appear widely dissimilar to the popular mind, and reduce them to one fundamental process. Thus recent psychology draws no sharp distinction between perception and recollection. It finds in both very much the same elements, though combined in a different way. Strictly speaking, indeed, perception must be defined as a presentative-representative operation. To the psychologist it comes to very much the same thing whether, for example, on a visit to Switzerland, our minds are occupied in perceiving the distance of a mountain or in remembering 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 reproduction 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 distinguished by the popular mind, so a thorough investigation of the flaws in these operations, that is to say, the counterfeits of knowledge, will probably lead to an identification 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, whatever its external form. Our next step, then, would appear to be to determine these differences 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 employed 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 hallucination 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[1], is a valuable 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, moreover, 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 hallucination, as thus defined, is a very narrow one. In by far the largest number of hallucinations it is impossible to prove that there is no modicum of external agency co-operating in the production of the effect. It is presumable, indeed, that many, if not all, hallucinations have such a basis of fact. Thus, the madman who projects his internal thoughts outwards 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 stimulations to which the organ is always exposed, even in profound silence, and which in his case assume an exaggerated intensity. And even 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 to 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.[2]
For these reasons, I think it best not to make the distinction between illusion and hallucination the leading principle of my classification. However important psychologically, it does not lend itself to this purpose. The distinction must be kept in view and illustrated as far as possible. Accordingly, while in general following popular usage and employing the term illusion as the generic name, I shall, when convenient, recognize 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 if they are, psychologically considered, identical operations, perception and memory are in general sufficiently marked off by a speciality in the form of the operation. Thus, while memory is the reproduction of something with a special reference of consciousness to its past existence, perception is the reproduction of something with a special reference to its present existence as a part of the presented object. In other words, though largely representative when viewed as to its origin, perception is presentative in relation to the object which is supposed to be immediately present to the mind at the moment.[3] Hence the convenience of recognizing the popular classification, 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 purpose dealing with the knowledge of other's 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 knowledge, 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 tenaciously and on which we are ready to act, which, to the mature mind, wear the appearance of intuitive truths, owing their cogency to nothing beyond themselves. A man's belief 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 perception, 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 differences in the degree of their immediacy. Thus it is manifest, after a moment's reflection, 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 fundamentally and essentially so than the proposition, "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 referable 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 origin 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 necessary to the production of such error. And, indeed, it is probable that most persons, antecedently 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 distinguishing between a past real event and a mere phantom of the imagination, illustrated in the exclamation, "I either saw it or dreamt it," sufficiently shows that memory is liable to be imposed on. Finally, it is agreed on 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 favourite 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-perception. 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 obvious 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.[4]
I would add that, in close connection with the first division, illusions of perception, I shall treat the subtle and complicated phenomena 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, "visions," shows, largely simulations of external, and more especially visual, perception.
Dreams are no doubt sharply marked off from illusions of sense-perception by a number of special circumstances. Indeed, it may be thought that they cannot be adequately treated in a work that aims primarily 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 feature 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.
CHAPTER III.
ILLUSIONS OF PERCEPTION: GENERAL.
The errors with which we shall be concerned in this chapter are those which are commonly denoted by the term illusion, that is to say, those of sense. They are sometimes called deceptions of the senses; but this is a somewhat loose expression, suggesting 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-illusions 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 operation in its most complete form, namely, that of visual perception.
I may observe that in this analysis of perception I shall endeavour 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[6] may be, we must accept the psychological fact that the concrete 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 science.
Psychology of Perception.
Confining ourselves for the present to the mental, as distinguished 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 delicious coolness, it is not difficult to show that he is really performing an act of mental synthesis, or imaginative construction. To the sense-impression[5] which his eye now gives him, he adds something which past experience has bequeathed to his mind. In perception, the material of sensation is acted on by the mind[2q], which embodies in its present attitude all the results of its past growth. Let us look at this process of synthesis a little more closely.
When a sensation arises in the mind, it may, under certain circumstances, go unattended to. In that case there is no perception. 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 obscure consciousness, but to the higher sensations connected with the 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 distinctness. 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 impression of the colour orange, the first consequence of attending to it is to mark it off from other colour-impressions, including those of red and yellow. And in recognizing the peculiar quality of the impression by applying 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 circumstances, 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 percept. Without going into the philosophical 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 sensations 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.[6] 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[4] distinctly calls the perception of distance an unconscious inference or a mechanically performed act of judgment.
I have hinted that these recovered sensations include the feelings we experience in connection with muscular activity, as in moving our limbs, resisting or lifting heavy bodies, and walking to a distant object. Modern psychology refers the eye's instantaneous recognition of the most important elements 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 constitute the substantial background of our percepts.
Another thing worth noting with respect to this process of filling up a sense-impression 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.[7]
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 a certain 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 colour to such an object involves the inclusion of a quality answering to the sensation, as brightness, or blue colour, 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 colour, except when there are circumstances present which are fitted to yield us those simple muscular and tactual experiences through which the ideas of a particular form, size, etc., are pretty certainly obtained.
The second step in this process of presentative construction is the recognition of an object as one of a class of things, for example, oranges, having certain special qualities, as a particular taste. In this step the connections of experience are less deeply organized, and so we are able to some extent, by reflection, to recognize it as a kind of intellectual working up of the materials supplied us by the past. It is to be noted that this process of recognition involves a compound operation of classifying impressions as distinguished from that simple operation by which a single impression, such as a particular colour, is known. Thus the recognition of such an object as an orange takes place by a rapid classing of a multitude of passive sensations of colour, 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 individual objects, as Westminster Abbey, or a friend, John Smith. The amount of experience 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.
If the recognition of an object as one of a class, for example, an orange, involves a compound 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 recognition, specific and individual, takes place by a consciousness of likeness amid unlikeness. 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 observed. 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 eye, of distance, and so on, which very distinctly affect the visual impression at different times. Yet the fact of our instantly recognizing a familiar object in spite of these fluctuations of appearance, proves that we are able to overlook 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 inference. To recognize an object as one of a class is often a matter of conscious reflection and judgment, even when the class is constituted by obvious material qualities which the senses may be supposed to apprehend immediately. Still more clearly does perception 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 applies still more forcibly to individual recognition, which is often a matter of very delicate 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 allow of our drawing a hard and fast line between them.
Finally, it is to be noted that these last stages of perception bring us near the boundary 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 individual experience is seen yet more plainly in the case of individual recognition. To identify an object, say a particular person, commonly presupposes some previous experience or knowledge of this object, and the existence 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 transition from common perception to individual recollection.[8]
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 preperception, the other that of perception proper.[9] In the first the mind holds itself in a passive attitude, except in so far as the energies of external attention are involved. The impression 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 may 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 mould or framework to the impression. This appears to involve an intensification of the mental image, transforming it from a representative to a presentative mental state, making it approximate somewhat to the full intensity of the sensation. In many of our instantaneous perceptions these two stages are indistinguishable to consciousness. Thus, in most cases, the recognition of size, distance, etc., takes place so rapidly that it is impossible to detect the two phases here separated. But in the classification of an object, 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[3q] required. Thus, the more frequently a similar 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[5] well remarks, "The artist sees details where to other eyes there is a vague or confused mass; the naturalist sees an animal where the ordinary 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.
