Page:Mind (Old Series) Volume 12.djvu/35

22 PROF. W. JAMES : Eevert to the case of two excited points on a surface with an unexcited space between them. The general result of previous experience has been that when either point was impressed by an outward object, the same object also touched the immediately neighbouring parts. Each point has thus its own local-sign associated with those of a circle of sur- rounding points, the association fading in strength as the circle grows larger. Each will revive its own circle ; but when both are excited together, the strongest revival will be that due to the combined irradiation. Now the tract joining the two excited points is the only part common to the two circles. And the feelings of this whole tract will therefore awaken with considerable vividness in the imagination when its extremities are touched by an outward irritant. The mind receives the impression of two distinct points, joined by an ideal line. The twoness of the points comes from the contrast of their local-signs : the line from the associations into which experience has wrought these latter. If no ideal line arises we have duality without sense of interval ; if the line be excited actually rather than ideally, we have the in- terval given with its ends, in the form of a single extended feeling. E. H. Weber, in the famous article in which he laid the foundations of all our accurate knowledge of these subjects, laid it down as the logical requisite for the percep- tion of two separated points, that the mind should, along with its consciousness of them, become aware of an unexcited interval as such. I have only tried to show how the known laws of experience may cause this requisite to be fulfilled. Of course, if the local signs of the entire region offer but little qualitative contrast inter se, the line suggested will be but dimly defined or discriminated in length or direction from other possible lines in its neighbourhood. This is what happens in the back, where consciousness can sunder two spots, whilst only vaguely apprehending their distance and direction apart. The relation of position of the two points is the suggested line. Turn now to the simplest case, that of a single ceivable that association and similarity itself should here have one and the same neural basis. If we suppose the sensory nerves from those parts of the body beneath any patch of skin to terminate in the same sensorial brain- tract as those from the skin itself, and if the excitement of any one fibre tends to irradiate through the whole of that tract, the feelings of all fibres going to that tract would presumably both have a similar intrinsic quality, and at the same time tend each to arouse the other. Since the same nerve- trunk in most cases supplies the skin and the parts beneath, the anatomical hypothesis presents nothing improbable.