§ 4. Perception of the Organism as Extended.— Up to this point, we have been dealing with the further development of a spatial perception which has already attained considerable advancement. The blind persons we have been speaking about were already so far advanced that, by purely synthetic or passive touch, they could obtain at least a vague and schematic apprehension of the shape even of unfamiliar objects. Also it is evident that the movements which they use in the exploration of objects have already acquired a more or less definite spatial value. For example, the relative degree of separation between finger and thumb means for them corresponding spatial distances. We have now to go further down in the scale of development, and to trace the rudimentary beginnings of spatial perception. This will be best done by considering the way in which we come to perceive our own body as extended. On this point I may quote Professor Croom Robertson. "I have not the slightest doubt that the first object that we become aware of as resisting, and at the same time spread out, is our own body. Of course, the child from the very beginning sees as well as touches, but I am putting aside vision for the present, and suppose that we have a child, at first unable to discern a difference between subject and object, beginning to acquire objective experience by way of touch. And I say . . . that the first object it would come to apprehend vaguely is not any other body, but its own. That one object it has always with it; other objects come and go, but it has always the power of touching its own body and thus of finding the activity of its own hand impeded."*

* Elements of Psychology, pp. 113114. Psych.

He also points out with great distinctness one important circumstance which immensely facilitates spatial perception in the case of our own body and its absence in the case of other bodies. This is the fact of double contact. "There is this special feature in "the child's" tactile experience of its own body, that whereas in touching another body it has an intensification of touch on the hand through which it is exerting pressure, in pressing the hand against its own face it gets, in connexion with the activity put forth and resisted, an intensification of two touches: it both touches and is touched. This gives peculiar and better data for the ordering of touch sensations. If, as we have reason to suppose, there is a qualitative difference of touch in every part of the body, then the child cannot but have its attention drawn to this, that through the fingers it has a variety of touches according to the part touched, both by way of the latter and also of the part that touches. Thus it is helped to finding its body as extended in this double way of learning to discriminate different parts, a way in which it is not helped when touching anything else."*

There is yet another consideration of paramount importance which should always be borne in mind when the perception of the organism is in question. Cutaneous sensation does not wholly depend on contact of the skin with an external object. Such contact gives what Robertson calls an intensification of touch; but the sensitive surface of the skin is normally in a state of excitation, apart from its occasional contact with external bodies. We have only to attend to any special area of the tactile surface, to detect the presence of cutaneous and temperature sensations. Besides this, an external body moving over the skin often leaves behind it in the path which it has traversed an after-sensation, which lasts for an appreciable time. Thus in the case of the organism, synthetic and analytic touch are combined as they cannot be combined in the case of external bodies. In the case of external bodies, active exploration of the parts of a whole, and simultaneous contact with the whole, cannot coexist; so that synthetic and analytic touch can only come into play alternately; but when the fingertip passes over a tactile surface, we have not merely a series of successive touches, but also a persistent sensation over the whole of the surface explored. By continual exploration of the body in various directions, this synthetic touch, which has its organ in the surface touched, acquires a spatial significance. There thus arises a direct senseperception of the configuration of the body and its parts which is always with us, whatever other spatial perception we may or may not have at any moment. This primitive spatial presentation of our own bodies is of great importance as a preparation for the perception of spatial relations in external bodies. Owing to it, both synthetic and analytic touch as applied to external bodies have from the outset a certain spatial significance. Take for example the act of grasping an object between finger and thumb. When the object grasped is a part of our own organism, such as the hand or the leg, the skin surface which lies between the contact of the thumb and the contact of the finger, is itself the seat of cutaneous sensation which has acquired spatial significance. Thus the interval between finger and thumb is directly perceived as an extended whole by synthetic touch. The extension is greater or less according as the thumb and finger are more or less widely apart. Hence, when an external body is taken between finger and thumb, the interval between them and the variations in the amount of this interval already stand for spatial distance and its varying degrees. There is yet one experience which we have not considered, that in which one cutaneous area is passively imposed upon another, as when one hand is laid on the other. Here there are two contacts; but it does not appear that they are usually discriminated. Supposing that perceptual development is so far advanced that both have spatial significance, the perception is not of two surfaces but of a common surface. If the two hands are in contact, this surface may be regarded either as the surface of the left hand or of the right, or of both simultaneously. The sensations in each surface contribute to the result. Now in the case of external objects one surface alone can be applied. But the spatial perception will be the more full and distinct, because of previous contact between surfaces both of which are sensitive. Further, when one part of the skin comes in contact with another, the area touched is apprehended as part of a wider area surrounding it; or rather of two wider areas surrounding it. For instance, when the palm of one hand is laid upon the palm of the other, the area of contact is apprehended both as a portion of the total surface of the right hand and arm, and as a portion of the total surface of the left hand and arm. When the palm of the hand is applied to an external object, the area of contact is immediately perceived by synthetic touch as part of the total surface of the hand and arm. It is not directly apprehended by synthetic touch as only a portion of the surface of the external body. But previous experiences of the kind in which one hand is laid on the other must constitute a certain preparation for regarding the area of contact as a portion not only of the body surface, but of the surface of the object touched; and it must therefore help to give significance to the active movements by which other parts of the external object are explored.