This (it seems to me) will be admitted, and will (I trust) be made still more plausible in the chapter on the Perception of Space.But the later developments of this perception are so complicated that these simple principles get easily overlooked.One of the complications comes from the fact that things move , and that the original object which we feel them to be splits into two parts, one of which remains as their whereabouts and the other goes of as their quality or nature.We then contrast where they were with where they are.
If we do not move, the sensation of where they were remains unchanged; but we ourselves presently move, so that that also changes;
and I where they were' becomes no longer the actual sensation which it was originally, but a sensation which we merely conceive as possible.Gradually the system of these possible sensations, takes more and more the place of the actual sensations.'Up' and 'down' become 'subjective' notions;
east and west grow more 'correct' than 'right' and 'left' etc.; and things get at last more 'truly' located by their relation to certain ideal fixed co-ordinates than by their relation either to our bodies or to those objects by which their place was originally defined.Now this revision of our original localizations is a complex affair; and contains some facts which may very naturally come to be described as translocations whereby sensations get shoved farther of than they originally appeared.
Few things indeed are more striking than the changeable distance which the objects of many of our sensations may be made to assume.A fly's humming may be taken for a distant steam-whistle;
or the fly itself, seen out of focus, may for a moment give us the illusion of a distant bird.The same things seem much nearer or much farther, according as we look at them through one end or another, of an opera-glass.Our whole optical education indeed is largely taken up with assigning their proper distances to the objects of our retinal sensations.An infant will grasp at the moon; later, it is said, he projects that sensation to a distance which he knows to be beyond his reach.In the much quoted case of the 'young gentleman who was born blind,' and who was 'couched' for the cataract by Mr.Chesselden, it is reported of the patient that "when he first saw, he was so far from making any judgment about distances, that he thought all objects whatever touched his eyes (as he expressed it) as what 'he felt did his skin." And other patients born blind, but relieved by surgical op- eration, have been described as bringing their hand close to their eyes to feel for the objects which they at first saw, and only gradually stretching out their hand when they found that no contact occurred.Many have concluded from these facts that our earliest visual objects must seem in immediate contact with our eyes.
But tactile objects also may be affected with a like ambiguity of situation.
If one of the hairs of our head be pulled, we are pretty accurately sensible of the direction of the pulling by the movements imparted to the head. But the feeling of the pull is localized, not in that part of the hair's length which the fingers hold, but in the scalp itself.This seems connected with the fact that our hair hardly serves at all as a tactile organ.In creatures with vibrisse, however, and in those quadrupeds whose whiskers are tactile organs, it can hardly be doubted that the feeling is projected out of the root into the shaft of the hair itself.We ourselves have an approach to this when the beard as a whole, or the hair as a whole, is touched.We perceive the contact at some distance from the skin.
When fixed and hard appendages of the body, like the teeth and nails, are touched, we feel the contact where it objectively is, and not deeper in, where the nerve-terminations lie.If, however, the tooth is loose, we feel two contacts, spatially separated, one at its root, one at its top.
From this case to that of a hard body not organically connected with the surface, but only accidentally in contact with it, the transition is immediate.With the point of a cane we can trace letters in the air or on a wall just as with the finger-tip; and in so doing feel the size and shape of the path described by the cane's tip just as immediately as, without a cane, we should feel the path described by the tip of our finger.Similarly the draughtsman's immediate perception seems to be of the point of his pencil, the sur- geon's of the end of his knife, the duellist's of the tip of his rapier as it plunges through his enemy's skin.When on the middle of a vibrating ladder, we feel not only our feet on the round, but the ladder's feet against the ground far below.If we shake a locked iron gate we feel the middle, on which our hands rest, move, but we equally feel the stability of the ends where the hinges and the lock are, and we seem to feel all three at once.
And yet the place where the contact is received is in all these cases the skin, whose sensations accordingly are sometimes interpreted as objects on the surface, and at other times as objects a long distance off.
