Tactile sensation

“ 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 ”

“ 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 ”

“ 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. ”

“ It is clear from the facts detailed that the nervous apparatus447 by which in the normal state sensations of touch are excited is that by which external influences determine the movements of the body in the abnormal state. But does the state of consciousness, which we term a tactile sensation, accompany the operation of this nervous apparatus in the abnormal state? or is consciousness utterly absent, the man being reduced to a pure mechanism? ”

“ Some forms of tactile sensation, also, would seem to remain ever sensitive, for, although it may be possible to become so inured to pain as to ignore it, yet that is probably a mental act, and it is said, moreover, that men have been tortured to death by the tickling of the soles of their feet. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ 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. ”

“ 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 ”

“ But they have all failed to notice with what peculiar intensity muscular movements call surface-sensibilities into play, and how largely the mere discernment of impressions depends on the mobility of the surfaces upon which they fall.
Our articular surfaces are tactile organs which become intensely painful when inflamed. Besides pressure, the only stimulus they receive is their motion upon each other. To the sensation of this motion more than anything else seems due the perception of the position which our limbs may have assumed. ”

“ 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. ”

“ 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. ”

“ English idealism sought to reserve to tactile perception a monopoly of the extended, the other senses dealing with space only in so far as they remind us of the data of touch. A more attentive psychology reveals to us, on the contrary, and no doubt will hereafter reveal still more clearly, the need of regarding all sensations as primarily extensive, their extensity fading and disappearing before the higher intensity and usefulness of tactile, and also, no doubt, of visual, extensity. ”

“ 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. ”

“ When the palm of the hand is gently tickled, as the finger passes rapidly and repeatedly over the palm, the parts first affected are again affected with various degrees of pressure, as the ear, in melody, is successively affected by repeated varieties of vibration; and various parts of the organ of touch exist, at the same moment, in various states, forming one joint result of sensation, as, in harmony, various vibrations of the organ of hearing co-exist, and blend together in one mingled delight. To produce tickling, a certain rapidity of succession is necessary ”

“ 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. ”

“ As I have already shown you, the knowledge of resistance and of weight which we gain through our tactile sense is derived from our own perception of exertion; and in vision, as in hearing, it is the force with which the undulations strike the sensitive surface that affects our consciousness with sights or sounds. ”

“ 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 ”

“ 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 ”

“ 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. ”

“ Pure tactile feelings are necessarily rare, since temperature sensations and muscular sensations are more or less combined with them. The organs of touch are found chiefly in the epidermis of the skin and certain underlying nervous structures. ”

“ By this means, we hoped to have the opportunity of discovering the nature of the sensibility subserved by the afferent fibres of the nerves to the muscles and other deep structures. The result far exceeded our expectation. We found that deep sensibility is an important factor in the sum of afferent impulses which pass into the central nervous system. For the impulses conducted by the afferent fibres of these deep nerves underlie our sensations of tactile and painful presure, of the locality of deep touch, and of the position of the parts in space. ”

“ Mere warmth, odour, relish, touch, sound, colour, contain no elements of extension. The co-operation with moving energy is what introduces us to the object world.
How then does Sensation aid muscularity in evolving Extension? In various ways, but chiefly thus. Our movements are not performed in vacuo, but in conjunction with sensation. The movements of the hand and arm, are usually conjoined with sensations of touch. We draw the hand across a table; there is an arm sensibility, purely motor or energetic, which is distinct from every mode of passive sensation. ”

“ Shut your eyes, and get a friend to prick the back of your hand with the two points of a pair of compasses simultaneously, so that the two points may be about the eighth of an inch apart when they touch you; you will feel—and if you could not correct the inference by the sense of sight, you would infer—that only one point is pricking you. The reason is that the skin of the back of the hand only reports one sensation ”

“ For suppose, to begin with, as Berkeley did, that all perception of extensity is to be referred to the sense of touch. We may, indeed, if you will have it so, deny extension to the data of hearing, smell and taste; but we must at least explain the genesis of a visual space that corresponds to tactile space. It is alleged, indeed, that sight ends by becoming symbolic of touch, and that there is nothing more in the visual perception of the order of things in space than a suggestion of tactile perception. ”

“ The answer is, that it is nothing more nor less than the antecedent mental image of the movement to be executed. We constantly receive nerve-impulses by the sensory nerves which have their source in the skin, joints, tendons, and muscles; these impulses fuse into an aggregate sensation which informs us about the varying positions of our limbs. Like other sensations, this leaves behind it a mental image, and it is this mental image, brought up as the last result of the play of association, which immediately precedes the external movement and constitutes the "feeling of innervation." ”

“ Whether touch be a sense delicate enough to discern such differences, would be, of course, a question for psycho-physics to decide,—and a question not simply of magnitudes, but of qualities of sensation. Perhaps it is not yet even legitimate to suppose that, just as by ear we can distinguish the qualitative differences of a million voices, so by touch we might be able to distinguish qualitative differences of surface scarcely less delicate. ”

“ 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. ”

“ 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. ”

“ Although there is still a good deal of uncertainty respecting the exact composition of the feelings of movement, it may be taken as fairly proved that they include an active element or "feeling of innervation," which is correlated with the central excitation of motor fibers, and a passive element or tactual sensation which is connected with a reflex excitation of sensory fibers, consequent on certain differences in the tensions and mutual pressure of various parts of the skin which result from the movement. ”

“ Press one of the eyeballs into a strained position with the finger, and objects move and are translocated accordingly, just as when prisms are used.
Curious illusions of movement in objects occur whenever the eyeballs move without our intending it. We shall learn in the following chapter that the original visual feeling of movement is produced by any image passing over the retina. Originally, however, this sensation is definitely referred neither to the object nor to the eyes. ”

“ 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. ”