The Foundations of Normal and Abnormal Psychology/Part 1/XXI
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Primary and Secondary Sensory Elements
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If we inspect the percept more closely, we find that there is some important difference in the character of the various constituent sensory elements. The central elements forming the nucleus of the percept are given directly by the sense-organ stimulated by its appropriate sensory stimuli, while the subordinate sensory elements are given indirectly,―they cannot be traced to appropriate sensory stimuli exciting those particular sense-organs on the activity of which those subordinate elements depend for their manifestation. In perceiving the lump of ice I can see the color, the size, the volume, the smoothness, the transparency, the distance, and even the weight and coldness. Now what I can see directly is only the color, transparency, size, as given immediately by the stimulated sense-organ, by the visual sensations and image on the retina. Whence I then come the rest of the sensory elements so distinctly experienced? They are not memory elements, ―they have the same sensory characters as the elements given by the direct impression of the sense-organs. It is not that on perceiving a certain transparent object we remember its volume, its distance, its smoothness, its resistance, we perceive all that in sensory terms. They are not images, ideas, or representations―they are sensations. The central sensory elements may be termed direct or primary, while the subordinate elements may be termed indirect or secondary. The percept then may be regarded as consisting of two classes of elements of sensations, the primary and secondary sensory elements.
The secondary sensory elements are not images, nor ideas, nor representations, different terms employed for the same state by various writers, the secondary elements of the percept are essentially sensations. Now sensations are qualitatively different from images, ideas or representations. The image of a light does not shine, the idea of a voice does not sound, and the representation of a perfume does not smell. A sensation, or presentation as it is sometimes termed, differs from an image or representation qualitatively, fundamentally. The sensation or presentation is given as immediate experience, while the image, the representation is essentially mediate, it is a mental substitute for the immediate experience of the sensation. The idea or image bears the same relation to the sensation as a photograph bears to the original, or rather as a symbol to the thing it represents. Ideas, images, representations substitute, represent sensations, but they are not sensations. A sensory process is fundamentally different. A sensation is not an intense idea, nor is an idea a weak sensation. Ideas differ far more qualitatively from sensations than visual sensations, for instance, differ from olfactory sensations. There is not a particle of evidence to substantiate the view that ideas or images are copies of sensations in the sense of being weak sensations or 'centrally excited sensations. There is nothing of the sensory in the idea. The weakest sensation cannot compare with the most vivid representation.
The laboratory experiments on that subject (Münsterberg and Külpe) are inconclusive as they either deal with incompletely perceived impressions, or with minimal sensations. In either case the percept is incomplete and uncertain. Külpe himself is forced to admit that ideas or 'centrally excited sensations' as he terms them "cannot be regarded as simple revivals of peripherally excited contents, if only for the reason, that their remaining attributes are very rarely indeed identical with those of perception." He then goes on making a fatal admission: "The most striking evidence of disparity is perhaps afforded by intensity. . . . It is only in special cases that centrally excited sensations can rise from their accustomed faintness to the vividness of sense perception. We then speak of them as hallucinations (?) ; and they enter into a disastrous competition with the real material of perception, completely transcending the boundary line which so usefully divides it from the material of imagination." Külpe admits that there is no intensity to the image, that there is no variation in 'intensity' of images, an 'attribute' characteristic of percepts. Psychologically regarded, this in itself shows the qualitative difference between image and percept.
In spite of the fact that Bergson is interested in psychology from a purely metaphysical standpoint, he nevertheless has some excellent remarks on memory and on the qualitative difference between image and percept. Although he is wrong in supposing that the image may be prolonged and projected into perceptual consciousness, he none the less emphasizes strongly the qualitative difference of the two. If I understand him aright he is opposed to the view of identification of memory images with sensations. A memory image is not a weakened sensation. "The absurdity" says Bergson "becomes patent when the argument is inverted (although this ought to be legitimate on the hypothesis adopted), that is to say, when the intensity of the sensation is decreased instead of the intensity of the pure memory being increased. For, if the two states (memory-image and sensation) differ merely in degree, there should be a given moment at which the sensation changed into a memory. If the memory of an acute pain, for instance, is but a weak pain, inversely an intense pain which I feel will end, as it grows less, by being an acute pain remembered. . . . Never will this weak state appear to me to be the memory of a strong state. Memory is something quite different."
Ideational and perceptual processes cannot be identified. The two are qualitatively different: the sensation ; has intensity, the image lacks it. We may point out i the main differences of sensation and image. (a) A sensation has intensity, an image totally lacks it. (b) An image is a reproduction or rather a representation, a symbol of a sensation, but no sensation represents another; a sensation, unlike an image, is not mediate, but immediate experience. (c) A sensation bears the mark of externality, an image lacks it. Finally (d) a sensation cannot be called up at will, while an image is independent of peripheral stimulations of external objects and is usually under the control of the will. No sensation differs so much from another as the image differs from its corresponding sensation.
Sensory elements and their synthesis, the percept, have motor tendencies, while the image or idea has not any motor tendencies. The reason why every image and idea has been made ideo-motor is because images or representations have been regarded as sensory in character, as weakened sensations, as 'sensationalettes' so to say. Bergson clearly sees the qualitative difference of the two; he insists on the non-motor character of the image in contradistinction to the strongly motor character of the sensation and the percept. Recently Thorndike laid great stress on the psychological fallacy of regarding images and ideas as motor in character. This fallacy is essentially due to the current identification of presentative and representative elements.
To refer as Külpe does to a hallucination as an intensified image is to reason in a circle and at the same time to be in sad contradiction with facts. A hallucination may be regarded as a fallacious percept, but it is not on that account an image; a hallucination is a percept and is essentially sensory in character. The fact of a percept being fallacious does not in the least imply that it is 'imaginary' and not sensory.
The ambiguity of the word 'imaginary' has not a little contributed to the psychological fallacy helping towards the confusion of image and sensation. 'Imaginary' is used in the common sense meaning not corresponding to any external reality, or in the psychological sense of consisting of those internal events or processes known as images or ideas. Now 'imaginary' used in the sense of lack of an external object by no means implies the psychological sense of consisting of images. A hallucination is commonly said to be imaginary in the sense of not having an objective reality, but we have to prove yet that it consists of images.
The theories of illusions, hallucinations as well as of dream states and hypnotic hallucinations are vitiated by that fundamental psychological fallacy. As a matter of fact hallucinations are not made up of images, but of sensory elements; while on the contrary hypnotic hallucinations are not made up of sensory elements, but of images. Hallucinations are not due to 'images' but to actual sensations. Psychologically regarded, hallucinations do not differ in their make-up from ordinary percepts. Ideas and images are not possessed of magic virtues, and with all the fancy work about them, they cannot display sensory qualities. The image or idea is that bloodless, shadowy, fluttering affair which can no more attain the life of a sensation than a written letter can attain the power of sound. Had it been otherwise the world would have been a large asylum for images to play their pranks in.
We may quote Stout as one of the few psychologists who seem not to accept the current psychological doctrine. In his Analytic Psychology he tells us "that complex perception does not consist in a given impression reviving a cluster of faint images of previous impressions." And again "impressional revival does not in the least countenance the theory that ideas are merely faint revivals of impressions. On the contrary, it tends strongly in the opposite direction. It shows that a revived impression is itself an impression, and not an idea." In his Manual of Psychology he says "that at bottom the distinction between image and percept is based on a difference of quality." And again, "percepts and images possess a relative independence. This can be accounted for, if we suppose that the nervous tracts excited in perceptual process are not wholly coincident with those excited in ideational process."
The elements of the percept are not ideational, not imaginary, they are essentially sensory. The perceptual elements are synthetized into one percept. To take our stock example, the ice. The lump of ice is experienced as one object with many qualities each of which furnishes respectively its sensory quota towards the formation of the whole of the perceptual experience. We see, we perceive the hard, heavy, smooth, resistant body of ice,―all the elements have alike the intensity of sensation. The hardness, the smoothness, the bodily resistance are perceived by the visual sense and are visual, but as such they, of course, differ from the sensations experienced by their appropriate sense organs, as when for instance the same sensations are given by touch or by muscular and kinesthetic sensations. Those muscular and tacto-motor sensations appearing as visual are not memory-images, but they are actual sensations, they are secondary sensations; they are secondary sensory elements which give the fullness of content to the percept, having visual sensory elements as its nucleus. Unlike memory-images, secondary perceptual elements have the immediacy of sensory experience. Remembered sensory qualities are not immediate experiences given in the object of perception.
If we turn to pathology, we find that cases closely confirm our view. In certain mental diseases the patient can perceive the various qualities, although he cannot represent them to himself. In other cases the patient can clearly and vividly represent objects in all their details, but he cannot perceive the objects, when directly confronted with them. Clinical cases, even if we exclude all facts from introspective study, clearly point to the qualitative difference of image and sensation, irrespective of the assumption of localization―they may be due to the function of different brain structures, or to different processes of the same brain structures. In the light of recent research it is more likely that the neuron structures underlying ideational processes differ from those subserving sensory processes. Whichever view however we entertain in regard to the anatomical structures all the facts go to prove that image and sensation are qualitatively different psychic events.
The percept is not ideational, but sensory. There are no memory-images in perceptual consciousness, although the latter may be closely associated with ideational processes. Such ideas, however, are on the fringe of the perceptual consciousness and do not constitute the essence of the percept. The percept consists of sensory elements, primary and secondary. The primary elements are initiated directly by incoming peripheral stimulations, while the secondary sensory elements are brought about indirectly, through the mediacy of the primary elements, the secondary elements themselves being really derived from sense-organs others than the ones directly stimulated by the peripheral excitation.
If the percept is visual, and V stands for the visual physiological processes, A for the auditory, O for the olfactory, M muscular, K kinaesthetic, T for tactual physiological processes; then let V1, M1, O1, K1, T1 stand for the primary sensory elements; and let V2, O2, M2, K2, T2 stand for the secondary sensory elements, then the total percept may be represented by the formula: V1O2M2K2T2. Since all the other elements appear in the visual percept under the visual aspect, we may represent the percept by the formula: V1 M2V1O2V1K2V1T2V1
The secondary sensory elements, though forming the main content of the percept, are apparently of a visual nature, and still they really belong to qualitatively different realms of sensations. This clearly reveals their origin and nature: the secondary sensory elements are not visual, but they become so by being initiated through the visual sense. In other words, secondary sensory elements are not peripherally initiated. Are they then centrally excited sensations? No. They can only be induced by an external stimulus. But that external stimulus must act indirectly, through another sense-organ.
- It may be well here to point out that the doctrine of primary and secondary sensory elements advanced by me has nothing in common with the primary and secondary qualities of the older psychologists.