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Boris Sidis, Ph.D., M.D.

© 1914




         The theory of perception is fundamental both in normal and abnormal psychology. All mental activities are intimately related with the process of perception. Our wills, our thoughts and our feelings relate to our experience of the outer world of things. Biologically regarded, the percept is of the most vital importance, inasmuch as it forms the medium between the individual and the outer environment. Psychologically, the percept reflects the external world and mirrors the conditions of life to which the given organism has to adjust itself. In fact, the percept may be regarded as the coin possessing the value of the external environment. In this respect we cannot help agreeing with Baldwin's statement: "The theory of perception is perhaps the most important as well as the most difficult problem in psychology. The interpretation of the higher processes of mind rests upon it and it underlies the body of our general philosophy. The great philosophies of the world take their rise from initial differences in the method of construing perception."

        In abnormal psychology the theory of perception is of the utmost importance, both from a theoretical and practical standpoint. Illusions, hallucinations, dream states, subconscious states, many states of dissociation depend for their explanation on the analysis of the process of perception. I have developed a theory of perception which may be characterized as the doctrine of primary and secondary sensory elements. This doctrine is based on a close analysis of the normal process of perception and is substantiated by observations and experiments of abnormal mental life.

        Before however we state our view of perception it may be well to make a review of what the principal psychological authorities teach on the subject.

        James Mill in discussing perception tells us: "The colors upon a body are different, according to its figure, its shape, and its size. But the sensations of color and the sensations of extension, of figure, of distance have been so often united, felt in conjunction that the sensations of the color are never experienced without raising the ideas of the extension; the figure, the distance in such intimate union with it, that they not only cannot be separated, but are actually supposed to be seen (italics are mine). The sight, as it is called of figure, or distance, appearing, as it does a simple sensation, is in reality a complex state of consciousness, a sequence in which the antecedent, a sensation of color, and the consequent a number of ideas are so closely combined by association that they appear not one idea, but one sensation."

        Sully defines perception as a mental act that ‘supplements a sense impression by an accompaniment or escort of revived sensations, the whole aggregate of actual and revived sensations being solidified or integrated into the form of a percept.' The revived sensations are equivalent to James Mill's associated ideas and images.

        We shall point out later the confusion which generally prevails among psychologists and psychiatrists, when they talk indiscriminately of revived sensations and ideas regarding the two as identical.

        Höffding describes the process of perception as the fusing of a reproduction and an actual sensation. The percept is thus conceived as compounded out of a representation and a sensation."

        Taine tells us that: "Images associated with the sensations of the different senses, especially with those of sight and touch constitute acquired perceptions."

        Wundt regards the percept as a psychical compound of ideas or of revived sensations or images. In that respect his analysis differs but little from that of other psychologists who regard the ideas, images, and revived sensations as identical elements going to form the associated whole or psychic compound, the percept.

        Külpe speaks of ‘centrally excited sensations' regarding them as the ideas and the images of the psychologists and psychiatrists, and tells us that he avoids the use of 'ideas.' As far as perception is concerned he closely follows his master, Wundt, and talks of psychic compounds, of sensations and centrally excited sensations which really are identical with the old ideas and images.

        Titchener follows closely Wundt and Külpe, and regards the 'percept as a compound, or a complex of sensations,' of peripheral and of centrally initiated sensations. In order to be explicit he hastens to tell us that there is no fundamental difference between the perception and idea. "It is customary to speak of perception, when the majority of the simple processes in the complex are the result of stimulation of a sense organ, i. e., are peripherally aroused, and of idea when the greater number are the result of an excitation within the brain cortex, i. e., are centrally aroused. If I have a table before me and my eyes open I am said to perceive the table; if I close my eyes and think of what I saw, to have an idea of a table. But we have seen that the sensations aroused centrally do not differ as psychological processes from those aroused peripherally." This statement put in such an explicit form brings out clearly what may be designated as the psychologist's fallacy. The fallacy becomes specially apparent in the domain of abnormal psychology.

        Baldwin with his characteristic breadth of comprehension puts the subject of perception on a wide basis: "Perception is the apperceptive or synthetic activity of mind whereby the data of sensation take on the forms of representation in space and time; or it is the process of the construction of our representation of the external world." Baldwin does not commit himself to the ordinary fallacy current among psychologists.

        Similarly James with his genius for psychological insight tells us: "The consciousness of particular material things present to sense is nowadays called perception." And again "Perception thus differs from sensation by the consciousness of further facts associated with the object of the sensation." He tells us further: "We certainly ought not to say what usually is said by psychologists and treat the perception as a sum of distinct psychic entities, the present sensation namely, plus a lot of images from the past, all integrated together in a way impossible to describe. The perception is one state of mind."

        We thus see that most of the psychologists regard the percept somewhat in Spencerian terms as being made up of presentations and representations, or as Spencer puts it as being 'partly presentative and partly representative.' In other words, the percept is a compound of sensations and images, a synthesis of peripherally induced sensations and of images, or of ideas centrally excited. One principle underlies the current theory of perception, variously phrased by different psychologists, and that is the identification of ideational and sensory processes.

        The identification of ideational and sensory processes may be traced to Spinoza when he tells us in his Ethics, Prop. XVII., note, "The modifications of the human body, of which the ideas represent external bodies as present to us, we will call the images of things" and then in another place of Part II., Prop. XLIX., note, "In order to illustrate the point let us suppose a boy imagining a horse and perceiving nothing else. Inasmuch as this imagination involves the existence of the horse, and the boy does not perceive anything which would exclude the existence of the horse he will necessarily regard the horse as present; he will not be able to doubt its existence, although he be not certain thereof. We have daily experiences of such a state of things in dreams." The images, according to Spinoza, are equivalent to sensations and percepts, unless counteracted by the more intense peripheral sensations which thus become the 'reductives' of the image, a doctrine afterwards fully developed by Taine. I may add that Spinoza's view of dreams is repeated almost verbatim by the greatest psychological authorities, all uncritically giving their assent to the current fallacy that the image is but a weakened sensation and that the sensation is an intensified image.

        This theory of images and perception is perpetuated through Hobbes, Locke, Hartley, Hume, James Mill down to our times.

        Hobbes in his terse English puts it: "Imagination therefore is nothing but decaying sense and is found in men and many other living beings, as well in sleeping as waking."

        Locke derives his 'ideas' from 'experience,' but his 'experience' is somewhat vague and broad, inasmuch as it flows from two fountain heads,―sensation and reflection. "Let us then suppose the mind to be as we say white paper void of all characters without any ideas, how comes it to be furnished? To this I answer in one word from experience. Our observation employed either about external sensible objects or about the internal operations of our minds, perceived and reflected on by ourselves is that which supplies our understanding with all the materials of thinking. These two are the fountains of knowledge from whence all the ideas we have or can naturally have, do spring." Perception is used by Locke in a broader sense than what it is understood at present, as he uses perception for sensory experience as well as for the introspection of higher mental processes. He tells us, however, that in either case "the mind has a power to revive perceptions which it has once had, with this additional perception annexed to them that it has had them before." Locke evidently entertains the view that sensations can be revived as original sensory experience and that the revived ideas do not differ, except for the addition of pastness, from the original ideas derived from the great source of sensation.

        When we pass to Hartley and Hume the identification of sensation and idea is set forth with great explicitness. In fact, it is taken as the fundamental principle of their psychological systems. Thus Hartley postulates in his eighth proposition that "Sensations by being often repeated leave certain vestiges, types or images of themselves which may be called simple ideas of sensation," and correspondingly we have "sensory vibrations, by being often repeated, beget in the medullary substance of the brain a disposition to diminutive vibrations which may be called vibratiuncles and miniatures corresponding to themselves respectively." The vibratiuncle is the physical substratum of what we experience as an idea, and is a copy of the original vibration. The vibratiuncle is a weakened vibration, and the idea is a weakened sensation.

        Hume does not burden himself with Hartley's vibrations and vibratiuncles, but still at the basis of his system we find the same fallacious psychological principle. "All our ideas" he says "are copies of our lively perceptions or impressions." In other words, our sensations are lively impressions, while the ideas are only weakened perceptions,―the idea differs from the sensation only in intensity. There is no qualitative difference between sensation and idea. Ideas belong to sensory processes and do not differ as such from sensations. This view has since become the heritage of current psychological theories.


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