This is the most commonly employed meaning of the term spatial. Yet it is evidently in its origin rather temporal than spatial. In ordinary movement we encounter by touch various obstacles, but only a very few of these impress us at any one moment of time. On the contrary, they succeed one after the other. To the blind, therefore, as Platner long ago remarked: Time serves instead of Space. In Vision, on the other hand, a large number, which it would take a very long time to encounter in touch, are presented simultaneously. In this there is an immense practical advantage, the result being that we come habitually to direct our every action by reference to the data of Sight. Now it is because these data—so simultaneously presented—are employed by us as the guides of action that their presentation acquires the character which we denominate Extensity. The simultaneous occurrence of a large number of Sounds does not seem to us to present such a character. But let us suppose that all the objects which constitute obstacles to our Activity emitted Sounds by which they were recognised; it is not doubtful that these would then come to be employed by us as the guides of our Activity and would acquire in our minds the character of Extensity. They would arrange themselves in a cotemporaneous, extensive, or spatial relation to one another just as the objects of Vision do at present.
It is only, therefore, when we come to employ the simultaneous presentation of Vision as the instrument of our Activity and the guide of Action that it acquires the character commonly called extensive. Successive visual sensations convey no extensive suggestion.
It is important to realise the nature of this peculiar feature in the data of Vision. The sounds which we hear, the odours which we smell, are the immediate result of certain undulations affecting the appropriate organ of sensation. We refer these to the object in which the undulations originate. In like manner a light which we see is referred to its objective luminous source. But light also and in addition is reflected from, and thus reveals the presence of the whole body of our resistant environment. Hence is derived the coloured presentation of Vision to which the character of extensity attaches. Nothing similar takes place in the case of the other distantial sensations. If sonorous undulations excited vibration in every resistant object of the environment they would undoubtedly come to arrange themselves in an order resembling the extensity suggested by Vision, though the slower rate of transmission of sound would detract from the practical simultaneity in the effect which, as we have seen, largely accounts for the perception of visual extensity. The universal diffusion of sunlight is also a determining factor.
The matter becomes still clearer when we contrast the experience of vident men with what we have been able to learn of the experiences of the blind. Nowhere have we found this aspect of the question discussed with the same clearness and ability as by M. Pierre Villey in his recently published essay, Le Monde des Aveugles—Part III.
The blind man, as he remarks, requires representations in order to command his movements. We must then penetrate the mind of the blind and ascertain what are his representations. Are they, he asks, muscular images combined by temporal relations, or are they images of a spatial order? He replies without hesitation: Both, but, above all, spatial images. It is clear, he says, that the modalities of the action of the blind are explained by spatial representations. These must be derived from touch. What, then, can be the spatial representations which arise from touch? The blind, he says, are often asked, How do you figure to yourself such and such an object, a chair, a table, a triangle? M. Villey quotes Diderot as affirming that the blind cannot imagine. According to Diderot, images require colour, and colour being totally wanting to the blind the nature of their imagination was to him inconceivable. The common opinion, says M. Villey, is entirely with Diderot. It does not believe that the blind can have images of the objects around him. The photographic apparatus is awanting and the photograph cannot therefore be there.
Diderot was a sensationalist. For this school, as Villey remarks, l'image est le décalque de la sensation, and he refers not merely to Condillac the friend of Diderot but to his continuator Taine whose dictum we have already quoted.
Diderot attempts to solve the problem by maintaining that tactual sensations occupy an extended space which the blind in thought can add to or contract, and in this way equip himself with spatial conceptions.
There would, on this view, as M. Villey remarks, be a complete heterogeneity between the imagination of the blind and that of the vident. M. Villey denies this altogether. He affirms that the image of an object which the blind acquires by touch readily divests itself of the characters of tactual sensation and differs profoundly from these. He takes the example of a chair. The vident apprehends its various features simultaneously and at once; the blind, by successive tactual palpations. But he maintains that the evidence of the blind is unanimous on this point, that once formed in the mind the idea of the chair presents itself to him immediately as a whole,—the order in which its features were ascertained is not preserved, and does not require to be repeated. Indeed, the idea divests itself of the great bulk of the tactual details by which it was apprehended, whilst the muscular sensations which accompanied the act of palpation never seek to be joined with the idea. This divestiture of sensation proceeds to such an extent that there is nothing left beyond what M. Villey calls the pure form. The belief in the reality of the object he refers to its resistance. The origin of each of these is exertional. The features upon which the mind dwells, if it dwells upon them at all, are les qualités qui sont constamment utiles pour la pratique—in a word, the dynamic significance of the thing.
