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Page:Popular Science Monthly Volume 65.djvu/235

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231
WHY IS THE HUMAN EAR IMMOBILE?

behind.[1] It can thus be seen that in accuracy of localization the ear can not be compared with the eye. The loss of the reflex apparatus by which the ear turned so as to catch most readily the vibrations in the air, has brought it about that the positions of sound are now so imperfectly apprehended by us.

The loss of this power of localization means two disadvantages. The first may be indicated in the words of Darwin:[2] "The power of erecting and directing the shell of the ears to the various points of the compass is no doubt of the highest service to many animals, as they thus perceive the direction of danger."

Closely connected with this practical disadvantage is another. The space of the ear has not the geometrical character of the spaces of sight and touch. Yet there is surely no good reason for doubting that it might have had much more of this character. Were the ear as mobile as the eye or the fingers, it would resemble them in the orderliness and well-defined character of the spatial forms it would yield. That its spatial form would equal in these respects that of the eye, it would be too much to affirm dogmatically. There may be more conditions to supply than merely that of mobility. Yet the touches from the less mobile parts of the body are singularly vague in their spatial outline as compared with those from the fingers and the tongue. And were the ear to gain mobility, we might expect to find it at least approximating, in its appreciation of form, to the senses which are regarded as so preeminently geometrical.

It is now apparent how serious are the disadvantages involved in the ear's immobility. Darwin thinks that the loss of the ear's movements is partly compensated by the increased ability to move the head about. It is true, these movements of the head are of importance both in seeing and in hearing. Yet in speaking of them as making up for the mobility of the sense-organs, we should be careful not to exaggerate their value. A man whose legs have been smitten with paralysis must find only small compensation for his affliction in the fact that a strong though somewhat slow porter is, when not otherwise occupied, ready to carry him about. It is also to be noticed that the eye has at its disposal the head movements, yet has retained its mobility.

We have now to ask what the mental gain is which has resulted from this loss. It is to be found in the ability to attend to a succession of sounds.

Let us notice how distinct is our perception of succession. A sound comes suddenly and sharply, and then it is gone, and another sound


  1. On the localization of sound, see 'Studies in Space Perception,' by A. H. Pierce.
  2. 'Descent of Man,' p. 14.