PHYSIOLOGICAL FACTORS OF THE ATTENTION-PROCESS. 355 mind, for it shows how the neural system corresponding to the object of attention concentrates in itself the energy liberated in all the afferent parts of the brain, and how, therefore, the quantity of energy concentrated in this system will be greater the greater is the quantity of free energy present in those parts of the brain. We have in a sense found an explanation of the singleness of the attention- process and of the focus of consciousness. In this connexion we may briefly consider the bearing of this result upon those strange cases of dual personality or double consciousness, in which two streams of presentation seem to pass simultaneously through two foci of consciousness without interaction or interference. The current explana- tion of such cases, which has been approved by so high an authority as Prof. Stout, is that all the organised systems of nervous elements which make up the chief part of the brain and which normally constitute one functional group, become divided in some way into two groups which function inde- pendently of one another. The view set forth above of the neural processes underlying the inhibitory aspect of the attention-process, makes possible a clearer conception of the way in which two systems of excitement might coexist in one brain. We have only to suppose that the paths which connect some group of upper level systems with the rest of the neural systems of the brain have their resting resistance so raised as to render impossible the drainage of energy from the one group to the other. The systems of one group, while remaining in the relation of reciprocal inhibition to one an- other, then cease to have this relation to those of the other group, and it becomes possible for any two systems belonging to the two different groups to be simultaneously active ; i.e., there are in one brain the neural conditions of two streams of presentations passing through two foci of consciousness. But although this current explanation of these cases is thus rendered more definite and very tempting by the adoption of the view of inhibition advocated above, I cannot regard the explanation as altogether satisfactory, because it assumes that the essential condition of the unity of individual consciousness is the spatial continuity of neural substance and neural process ; and this assumption, although it has been made by authors so distinguished as Fechner i and von Hartmann, 2 besides many others, I find great difficulty in accepting for reasons briefly indicated elsewhere. 3 1 Elemente d. Psiicho-Physik. 2 Philosophic d. Unbewussten. 3 " Proceedings of the Psychological Society," British Journal of Psy- chology, vol. i., part iii.
