Tactile perception

“ Perception of form comes from the combination of two sensations, tactile and muscular, muscular sensations being sensations of movement. What we call in the blind the tactile sense is in reality more often the stereognostic sense. That is, they perceive by means of their hands the form of bodies. ”

“ When to learn the form of an object we move the hand over it, muscular sensations are combined with proper tactile, and such a combination of the two sensations is frequent; moreover, we rarely touch anything without at the same time getting temperature sensations; therefore pure tactile feelings are rare. From an evolution point of view, touch is probably the first distinctly differentiated sensation, and this primary position it still largely holds in our mental life. ”

“ Supposing the ultimate organs of the sense of touch to be really congregated more thickly under the ridges than under the furrows—on which there has been some question—the power of tactile discrimination would depend very much on the closeness of the ridges. ”

“ This leads us to believe that what is seen is usually tangible, and that it has, whether we touch it or not, the hardness or softness which we should expect to feel if we touched it. But the mere fact that we are able to infer what our tactile sensations would be shows that it is not logically necessary to assume tactile qualities before they are felt. All that is really known is that the visual appearance in question, together with touch, will lead to certain sensations, which can necessarily be determined in terms of the visual appearance, since otherwise they could not be inferred from it. ”

“ This shows that the tactile sense is not in a very high stage of development, since it needs, when unhelped by long experience, the assistance of the sense of sight. Perceptions through touch alone, therefore, are of small importance ”

“ No part of the body except the point of the tongue is as sensible to touch as the tips of the fingers and the palm of the hand. Tactile discrimination is so acute as to be able to interpret to the brain significant impressions produced in very rapid succession. ”

“ For example, most of the visual objects in our neighbourhood rouse tactile images: we have a different feeling in looking at a sofa from what we have in looking at a block of marble, and the difference consists chiefly in different stimulation of our tactile imagination. ”

“ But this difference in the accessibility of phenomena is not due to their peculiar nature. It is connected with a different fact, with the modes of excitement which call them forth. If the visual sensation is common to all, it is because the exciting cause of the sensation is an object external to our nervous systems, and acting at a distance on all. [2] The tactile sensation is at the beginning more personal to the one who experiences it, since it requires contact ”

“ On the other hand, consider tactile space, limiting ourselves to the sensations of a single finger, that is in sum the assemblage of positions this finger can occupy. This tactile space that we shall analyze in the following section and which consequently I ask permission not to consider further for the moment, this tactile space, I say, has three dimensions. Why has space properly so called as many dimensions as tactile space and more than simple visual space? It is because touch does not operate at a distance, while vision does operate at a distance. ”

“ Moreover, as a matter of fact, it is certain that the muscular sense is so closely connected with both the visual and the tactile senses, that, by the ordinary laws of association, the ideas which it suggests must needs be common to both. ”

“ Then with the consciousness of that mobility, the notion of space of three dimensions—which is "Raum" or "room" to move with perfect freedom—is at once given. But the notion that the tactile surface itself moves, cannot be given by touch alone, which is competent to testify only to the fact of change of place, not to its cause. The idea of the motion of the tactile surface could not, in fact, be attained, unless the idea of change of place were accompanied by some state of consciousness, which does not exist when the tactile surface is immoveable. ”

“ Helen Keller's brain, as shown by her accomplishments in later life, was a remarkable one; not long after birth she became deaf and blind, consequently there was practically only one avenue of intelligence left open for the education of that brain, viz. the tactile kinæsthetic. But the tactile motor sense is the active sense that waits upon and contributes to every other sense. The hand is the instrument of the mind and the agent of the will; consequently the tactile motor sense is intimately associated in its structural representation in the brain with every other sense. ”

“ Obviously, there is no more likeness between the feel of a surface and the colour of it, than there is between its colour and its smell. All simple sensations, derived from different senses, are incommensurable with one another, and only gradations of their own intensity are comparable. And thus so far as the primary facts of sensation go, visual figure and tactile figure, visual magnitude and tactile magnitude, visual motion and tactile motion, are truly unlike, and have no common term. ”

“ It is even conceivable, if not exactly likely, that certain operators may have learned to think directly, so far as the purely conscious part of the process of thought is concerned, in terms of the tick-auditory symbolism or, if they happen to have a strong natural bent toward motor symbolism, in terms of the correlated tactile-motor symbolism developed in the sending of telegraphic messages. ”

“ How can the hand supply the place of the eye? The motor image gives the key to the problem. If the patient can read, so to speak, with his fingers, it is because in tracing the letters he gives himself a certain number of muscular impressions which are those of writing. In one word, the patient reads by writing (Charcot) : the feeling of the graphic movements suggests the sense of what is being written as well as sight would." [64]
The imagination of a blind-deaf mute like Laura Bridgman must be confined entirely to tactile and motor material. ”

“ It is obvious on this scheme that the cell which we have marked K may stand for the seat of either a resident or a remote sensation occasioned by the motor discharge. It may indifferently be a tactile, a visual, or an auditory cell. The idea of how the arm feels when raised may cause it to rise; but no less may the idea of some sound which it makes in rising, or of some optical impression which it produces. Thus we see that the 'mental cue' may belong to either of various senses; and that what our diagrams lead us to infer is what really happens ”

“ We gain a field of vision from an ensemble of local signs, and, as concerns tactile sense, the same thing happens, the functions of the corpuscles of touch being like those of the cones and rods of the retina in sight. ”

“ But in regard to the sense of touch, not only has he a superior provision in the tactile organs of the fingers, but the naked and soft condition of the skin renders it susceptible to contact in a degree not possessed by any other animals. ”

“ The limitation of the exercises of the tactile sense to the cushioned tips of the fingers, is rendered necessary by practical life. It must be made a necessary phase of education because it prepares for a life in which man exercises and uses the tactile sense through the medium of these finger tips. ”

“ Tactile sensibility, too, must be carefully allowed for. The sense of varying resistance in the air may reach in some seeing persons, as well as in the blind, a high degree of acuteness. [177]
But there are cases of sudden motor inhibition where no warning can well have been received from hyperæsthetic sensation, where we come, as it seems, to telæsthesia or to spirit guardianship. ”

“ Finally, before going on to our principal subject, we should glance at the instinctive chewing motions which were mentioned among tactile plays. When a full-grown man going for a walk sticks a twig in his mouth and gnaws it the movements of his own jaw are of more interest to him than is the stick, except as it promotes sensations of contact. ”

“ The tip of the tongue possesses the most acute sensibility of any portion of the body, and next in order are the tips of the fingers. The hands are the principal organs of tactile sensation. The nerves of general sensibility are distributed to every part of the cutaneous tissue. The contact of a foreign body with the back, will produce a similar tactile sensation, as with the tips of the fingers. The sensation, however, will differ in degree because the back is supplied with a much smaller number of sensitive filaments ”

“ For, while the physiology of the brain was more and more successful in localizing sensations and movements, but never ideas, the diversity of sensory aphasias obliged clinicians to break up the intellectual centre into a growing multiplicity of image centres—a centre for visual representations, for tactile representations, for auditory representations, etc.,—nay, to divide sometimes into two different tracks, the one ascending and the other descending, the line of communication between any two of them. ”

“ We can identify it with a differently located tactile and visual image of 'the joint' itself.
Just so when we feel the tip of our cane against the ground. The peculiar sort of movement of the hand (impossible in one direction, but free in every other) which we experience when the tip touches 'the ground,' is a sign to us of the visual and tactile object which we already [Pg 42] know under that name. We think of 'the ground' as being there and giving us the sensation of this kind of movement. The sensation, we say, comes from the ground. The ground's place seems to be its place ”

“ For example, the hairs and nails are utterly devoid of sensibility, as everyone knows. Nevertheless, if the ends of the nails or hairs are touched, ever so lightly, we feel that they are touched, and the sensation seems to be situated in the nails or hairs. Nay more, if a walking-stick a yard long is held firmly by the handle and the other end is touched, the tactile sensation, which is a state of our own consciousness, is unhesitatingly referred to the end of the stick ”

“ Pressure with the head of a pin on the normal skin produced a tactile sensation, together with sensations of slight cold and of hair-stimulation. On the affected area, the latter elements were no longer present, but the fundamental quality of the sensation seemed to remain the same, so that when the head of the pin was passed across the border separating the normal and affected areas, a considerable effort of attention was necessary to detect when the change occurred. The differences in quality were of such a kind that it is very improbable they would be noticed by any but a trained observer. ”

“ Our tactile imagination is put to play immediately. Our palms and fingers accompany our eyes much more quickly than in presence of real objects, the sensations varying constantly with the various projections represented, as of face, torso, knees; confirming in every way our feeling of capacity for coping with things,—for life, in short. I care little that the picture endowed with the gift of evoking such feelings has faults, that the types represented do not correspond to my ideal of beauty, that the figures are too massive, and almost unarticulated ”

“ By touching a body at various points, from the difference of pressure and from a comparison of the positions of various points in the tactile field we judge of the configuration of the body. A number of " tactile pictures " are obtained by pass ing the skin over the touched body, and the shape of the body is further determined by a knowledge of the muscular movements necessary to bring the cutaneous surface into contact with different portions of it. If there is abnormal displacement of position, a false conception may arise as to the shape of the body. ”

“ If both eyes be armed with prisms with their angle towards the right, we pass our hand to the right of all objects when we try rapidly to touch them. And this illusory sense of their position lasts until a new association is fixed, when on removing the prisms a contrary illusion at first occurs. Passive or unintentional changes in the position of the eyeballs seem to be no more kept account of by the mind than prisms are; so we spontaneously make no allowance for them in our perception of distance and movements. ”

“ More important still than the tactile sensations, properly speaking, are the sensations which pertain to what is sometimes called internal touch, deep-seated sensations emanating from all points of the organism and, more particularly, from the viscera. ”

“ The reacter awaits the signal and reacts if it is of one sort, but omits to act if it is of another sort. The reaction thus occurs after discrimination; the motor impulse cannot be sent to the hand until the subject knows what the signal is. The nervous impulse, as Mr. Cattell says, must probably travel to the cortex and excite changes there, causing in consciousness the perception of the signal. ”

“ In other connections we have touched upon many movement plays, such as voice practice and the production of sounds by means of various bodily organs, experimentation with tactile stimuli, and watching moving objects. This sort of exercise often combines motor with sensor play, as has been frequently pointed out. ”

“ But there is one effect which is not conjectural, and that is the sensation of touch. This effect, owing to physiological inference or perhaps to a reflex, is associated by us with the finger-tip. But the sensation is the same if, by artificial means, the parts of the nerve nearer the brain are suitably stimulated—e.g. if your hand has been amputated and the right nerves are skilfully manipulated. Thus our confidence that touch affords evidence of the existence of bodies at the place which we think is being touched is quite misplaced. As a rule we are right, but we can be wrong ”