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358 w. MCDOUGALL: fication of attention. For according to the acceptable doctrine of Prof. James l the idea or sensory representation of a move- ment is the immediate conscious antecedent of the move- ment, and it would appear that by volition we can but cause an idea of movement to realise itself, if the non-voluntarily arisen idea has failed to do so, or can cause an increase in the force of the muscular contractions if the idea of move- ment has realised itself non-voluntarily. How do we achieve this if not by a voluntary concentration of attention upon the idea of the movement ? The neural effect of this volun- tary concentration of attention can only be, in both cases, a fuller flow of energy from a system of neural elements which has been excited either through peripheral stimulation of its sensory extremities or through some association-path. In 'the case of willed movement the system constitutes at once the cortical ' centre ' for the initiation of that movement and the kinsesthetic ' sensory centre ' for the representation of the movement ; in the other case it is a system whose excitement underlies the rise to consciousness of some sensory presenta- tion or idea. Whatever may be the conditions of volition, this is its effect in the case of concentration of attention on the idea of movement, and familiarity should no more blind us to the inexplicable character of the effect than in the case of production of sensation by excitation of the elements of the sensory cortex. There is then, I submit, no a priori ground for making this great difference between ideas of movement and other ideas ; if volition can directly re-enforce the former class of ideas and if the neural effect is a fuller stream of energy issuing from the corresponding neural system, then we should be prepared to find that volition may have similar effects upon other ideas and upon the neural processes correlated with them. Clearly, it is for those who put apart ideas of movement, or the processes of innervation of muscles, in a class by them- selves to show cause for doing so, and I do not think that this has ever been done. On the other hand, the experi- ments reported in an earlier section of this paper (pp. 330 and 331) go some way to prove that we can exert direct volun- tary control over both ideas and sensations, in the sense that we can, without muscular adjustment or innervation, directly favour one mode of perception as against others or the pre- sence in consciousness of one quality of sensation. It seems clear that, in the case of voluntary re-enforcement 1 Principles of Psychology, vol. ii., p. 501.