Page:Mind (Old Series) Volume 12.djvu/22

 THE PEBCEPTION OF SPACE. (l.) 9 may also to a certain extent be explained by the operation of the same factor. It is an anatomical fact that the most spatially sensitive surfaces (retina, tongue, finger-tips, &c.) are supplied by nerve-trunks of unusual thickness, which must supply to every unit of surface area an unusually large number of terminal fibres. But the variations of felt ex- tension obey probably only a very rough law of numerical proportion to the number of fibres. A sound is not twice as voluminous to two ears as to one ; and the above-cited varia- tions of feeling, when the same surface is excited under dif- ferent conditions, show that the feeling is a resultant of several factors of which the anatomical one is only the prin- cipal. Many ingenious hypotheses have been brought for- ward to assign the co-operating factors where different con- ditions give conflicting amounts of felt space. Later we shall analyse some of these cases in detail, but it must be confessed here in advance that many of them resist analysis altogether. 1 1 It is worth while at this point to call attention with some emphasis to the fact that, though the anatomical condition of the feeling resembles the feeling itself, such resemblance cannot be taken by our understanding to explain why the feeling should be just what it is. We hear it untiringly reiterated by materialists and spiritualists alike that we can see no possible inward reason why a certain brain-process should produce the feeling of redness and another of anger : the one process is no more red than the other is angry, and the coupling of process and feeling is, as far as our understanding goes, a juxtaposition pure and simple. But in the matter of -spatial feeling, where the retinal patch that produces a triangle in the mind is itself a triangle, &c., it looks at first sight as if the sensation might be a direct cognition of its own neural condition. Were this true, however, our sensation should be one of multitude rather than of continuous extent ; for the condition is number of optical nerve-termini, and even this is only a remote condition and not an immediate condition. The immediate condi- tion of the feeling is not the process in the retina, but the process in the brain ; and the process in the brain may, for aught we know, be as unlike a triangle, nay, it probably is so, as it is unlike redness or rage. It is simply a coincidence that in the case of space one of the organic conditions, viz., the triangle impressed on the skin or the retina, should lead to a re- presentation in the mind of the subject observed similar to that which it produces in the psychological observer. In no other kind of case is the coincidence found. Even should we admit that we cognise triangles in .space because of our immediate cognition of the triangular shape of our excited group of nerve-tips, the matter would hardly be more transparent, for the mystery would still remain, why are we so much better cognisant of triangles on our finger-tips than on the nerve-tips of our back, on our eye than on our ear, and on any of these parts than in our brain? Thos. Brown very rightly rejects the notion of explaining the shape of the space perceived by the shape of the "nervous expansion affected". " If this alone were necessary, we should have square inches .and half inches, and various other forms, rectilinear and curvilinear, of fragrance and sound." (Lectures, xxii.)