Page:Mind (New Series) Volume 12.djvu/498

484 w. MCDOUGALL: no means indissolubly associated with, or necessary to, the voluntary determination of the changes. The influence of eye-movements on the mode of per- ception of such objects as figure 2 is very marked. It may be studied most conveniently and in its purest form in the after-images of such figures. When a clear after-image of figure 2 is obtained (in positive and negative after-images the effects are alike) movements of the eyes along the direction of any one of the three possible linear groupings greatly facilitate the appearance of that grouping, and by such movements the three linear groupings or any two of them may be made to alternate with one another regularly, or one grouping may be made to persist to the exclusion of all others for several seconds. We may note lastly in this connexion that activity of the eye-muscles favours the return to consciousness of the primary memory-image ; as Prof. Ward l writes, after a momentary glance at an object, " the object is imaged for a moment very vividly and distinctly, and can be so recovered several times in succession by an effort of attention. Such reinstatement is materially helped by rapidly opening and closing the eyes, or by suddenly moving them in any way." And he adds, "In this respect a primary memory-image resembles an after-sensation, which can be repeatedly revived in this manner when it would otherwise have disappeared ". My own experience bears out this statement entirely, and I would only add that the movement that has the most marked effect of this kind is a movement of convergence with accommodation. I turn now to the consideration of the physiological ad- justments in virtue of which the muscular activities are able to produce these effects. In this connexion I have no novel suggestion to make. I would merely attempt to render a little more definite and concrete the view of the process adopted by Dr. Maudsley, by Profs. Wundt, Kibot, James and others. This view may be stated shortly in Eibot's words : " As a motor organ the brain plays a complex role. In the first place, it inaugurates the movements that accom- pany perceptions, images or ideas ; afterwards, these move- ments, which frequently are intense, return to the brain by way of the muscular sense as sensations of movement ; the latter increase the quantity of available energy, 2 which on 1 Art. "Psychology," Encyclop. Brit., p. 59. 8 We see here that Ribot uses the conception of a common store of free energy in the afferent side of the nervous system, in much the same way as I have used it above.