§ 7. Origin of Spatial Perception. — When we began to discuss spatial perception at the beginning of the previous chapter, we propounded two questions. So far, we have only considered the first of these, relating to the development of the perception from more indefinite and imperfect to more definite and perfect forms. It is now time to take up the second inquiry. Do the same conditions which account for development of the spatial perception also account for its first origin? This seems at first sight at least abstractly conceivable. We may suppose at the outset on the one hand experience of mere extensity, and on the other experience of active movement. Neither of these experiences is in itself, properly speaking, spatial. Spatial relations begin to exist for consciousness only in so far as the experience of extensity combines with the experience of active movement in the manner which we have already described. If the combination is to begin with entirely absent, so that it only arises in the history of the individual consciousness, spatial perception has not only a psychological development but a psychological origin. If we adopt this view, we commit ourselves to what is called a genetic as opposed to a nativistic theory of spatial perception.

The corresponding nativistic view would assume the following form. From the outset of mental development there are certain connexions between experiences in the way of extensity and appropriate motor activity, — connexions not learnt by experience, but due to congenital constitution. So far as these original connexions exist, some kind of spatial perception is born with the individual, not acquired by him.

The evidence for the nativistic view is strong in the case of many animals. The chick, for instance, on emerging from its shell, pecks from the outset at a suitable object in such a way as to show that without the help of experience it is in some manner aware of the direction, situation, and distance of the object. It would seem therefore that with it spatial perception is to a large extent innate. Human beings, on the contrary, have to learn by a gradual process to discern the shape, situation, distance, etc., of objects. The higher animals, such as dogs and monkeys, go through a similar process, though not to nearly the same degree. But even in the case of human beings there is evidence that some original connexion exists between local sign experience and motor activity, though it may be at the outset very indefinite.* The evidence is strongest for sight. Apart from some congenital connexion, however indeterminate, between local sign experiences and movements, it is difficult to see how subsequent development in this respect could have a startingpoint. Thus the most probable conclusion is that a vague spatial perception is congenital even in human beings. So much may be conceded to the nativistic theory. But it will be clear from what we have said and are about to say that this original endowment only supplies a rudimentary startingpoint for a highly elaborate and complex development.

* It should be noted that what is congenital in the human being does not necessarily appear in the newborn infant. The nervous system of the newborn infant is very far from being fully grown. Much comes to it by mere physiological growth as distinguished from learning by experience. The same is also to some extent true of the newborn dog and other higher animals, though the growth in this case is much more rapid.