We shall learn in the chapter on Space that our feelings of our own movement are principally due to the sensibility of our rotating joints.Sometimes by fixing the attention, say on our elbow-joint, we can feel the movement in the joint itself; but we always are simultaneously conscious of the path which during the movement our finger-tips describe through the air, and yet these same finger-tips themselves are in no way physically modified by the motion.A blow on our ulnar nerve behind the elbow is felt both there and in the fingers.Refrigeration of the elbow produces pain in the fingers.Electric currents passed through nerve-trunks, whether of cutaneous or of more special sensibility (such as the optic nerve), give rise to sensations which are vaguely localized beyond the nerve-tracts traversed.Persons whose legs or arms have been amputated are, as is well known, apt to preserve an illusory feeling of the lost hand or foot being there.Even when they do not have this feeling constantly, it may be occasionally brought back.This sometimes is the result of exciting electrically the nerve-trunks buried in the stump.
"I recently faradized," says Dr.Mitchell, "a case of disarticulated shoulder without warning my patient of the possible result.For two year she had altogether ceased to feel the limb.As the current affected the brachial plexus of nerves he suddenly cried aloud, 'Oh the hand, -- the hand!' and attempted to seize the missing member.
The phantom I had conjured up swiftly disappeared, but no spirit could have more amazed the man, so real did it seem."
Now the apparent position of the lost extremity varies.Often the foot seems on the ground, or follows the position of the artificial foot, where one is used.Sometimes where the arm is lost the elbow will seem bent, and the hand in a fixed position on the breast.
Sometimes, again, the position is non-natural, and the hand will seem to bud straight out of the shoulder, or the foot to be on the same level with the knee of the remaining leg.Sometimes, again, the position is vague;
and sometimes it is ambiguous, as in another patient of Dr.Weir Mitchell's who "lost his leg at the age of eleven, and remembers that the foot by degrees approached, and at last reached the knee.When he began to wear an artificial leg it reassumed in time its old position, and he is never at present aware of the leg as shortened, unless for some time he talks and thinks of the stump, and of the missing leg, when...the direction of attention to the part causes a feeling of discomfort, and the subjective sensation of active and unpleasant movement of the toes.With these feelings returns at once the delusion of the foot as being placed at the knee."
All these facts, and others like them, can easily be described as if our sensations might be induced by circumstances to migrate from their original locality near the brain or near the surface of the body, and to appear farther off; and (under current circumstances)
to return again after having migrated.But a little analysis of what happens shows us that this description is inaccurate.
The objectivity with which each of our sensations originally comes to m, the roomy and spatial character which is a primitive part of its content, is not in the first instance relative to any other sensation.The first time we open our eyes we get an optical object which is a place, but which is not yet placed in relation to any other object, nor identified with any place otherwise known.It is a place with which so far we are only acquainted.When later we know that this same place is in 'front' of us, that only means that we have learned something about it, namely, that it is congruent with that other place, called 'front,' which is given us by certain sensations of the arm and hand or of the head and body.But at the first moment of our optical experience, even though we already had an acquaintance with our head, hand, and body, we could not possibly know anything about their relations to this new seen object.It could not be immediately located in respect of them.How its place agrees with the places which their feelings yield is a matter of which only later experience can inform us; and in the next chapter we shall see with some detail how later experience does this by means of discrimination, association, selection, and other constantly working functions of the mind.When, therefore, the baby grasps at the moon, that does not mean that what he sees fails to give him the sensation which lie afterwards knows as distance; it means only that he has not learned at what tactile or manual distance things which appear at that visual distances are. And when a person just operated for cataract gropes close to his face for far-off objects, that only means the same thing.All the ordinary optical signs of differing distances are absent from the poor creature's sensation anyhow.
His vision is monocular (only one eye being operated at a time); the lens is gone, and everything is out of focus; he feels photophobia, lachrymation, and other painful resident sensations of the eyeball itself, whose place he has long since learned to know in tactile terms; what wonder, then, that the first tactile reaction which the new sensations provoke should be one associated with the tactile situation of the organ itself? And as for his assertions about the matter, what wonder, again, if, as Prof.Paul Janet says, they are still expressed in the tactile language which is the only one he knows." To be touched means for him to receive an impression without first making a movement." His eye gets such an impression now;
so he can only say that the objects are touching it.'
"All his language, borrowed from touch, but applied to the objects of his sight, make us think that he perceives differently from ourselves, whereas, at bottom, it is only his different way of talking about the same experience.
