General average: S, 27.10 sec.; C, 34.62 sec.
Can anything be said, based on the reports, by way of explanation of the advantage which complexity gives? In the first place, the attitude of the subject towards his image seems to have been much the same as his attitude towards an external object: to his observation the image became, in fact, an object. "When the image was gone," says one, "my eyes seemed to be in search of something." And occasionally the one ideated object was felt to exert an influence over the other. "The complex seemed to affect the form of the simpler figure." "It seemed that the complex actually had the effect of diminishing the size of the simpler figure." From time to time the images varied, too, in distinctness, just as the objects of perception vary, and the superior distinctness of the more complex was frequently noted by the subjects. Now the importance of the boundary line in perception is well understood. It seems to have a corresponding importance here. "What I notice more in the simple figure," says one observer, "is the mass; in the complex, the outline." "The simple seemed to lose its form," says another, "the complex did not; the jagged edge was very distinct." And it is not improbable, in view of the reports, that irregularities involving change of direction and increase in extent of outline contributed mainly to the greater persistence of the more complicated image, the 'mass' being in both figures approximately the same. Nor did the advantage of the broken line escape the notice of the subject. "I found myself," is the comment of one, "following the contour of the star—exploring. The circle I could go around in a twinkle." Again, "the points entered the field before the rest of the figure." And again, "the angle is the last to fade away."
Fig. 2.
Now this mental exploration involves, of course, changes in the direction of the attention corresponding in some way to changes in the direction of the lines. Does this shifting of the attention involve ideated movements? There can be little doubt that it does. "I felt an impulse," says one, "to turn in the direction of the image seen." And the unconscious actual movements, particularly those of the eyes, which are associated with ideated movements, took place so often that it is hard to believe they were ever wholly excluded. Such movements, being slight and automatically executed, were not at first noticed. The subjects were directed, in fact, to attend in all cases primarily to the appearance and disappearance of the images, and it was only after repeated observations and questions were put, that they became aware of associated movements, and were able, at the close of an observation, to describe them. After that, it became a common report that the eyes followed the attention. And as we must assume some central influence as the cause of this movement, which while the eyes were closed could have no reflex relation to the stimulus of light, we must impute it to the character of the ideas, or to their physical substrates.
The idea, or, as we may call it, in view of the attitude of the subject, the internal sensory impression, thus seems to bear a double aspect. It is, in the cases noted, at once sensory and motor, or at any rate involves motor elements. And the effect of the activity of such motor elements is both to increase the distinctness of the image and to prolong the duration of the process by which it is apprehended. The sensory process thus stands in intimate dependence on the motor. Nor would failure to move the eyes or any other organ with the movement of attention, if established, be conclusive as against the presence of motor elements. A motor impulse or idea does not always result in apparent peripheral movement. In the suppressed speech, which is the common language of thought, the possibility of incipient or incomplete motor innervations is well recognized. But where the peripheral movement actually occurs it must be accounted for. And as the cause here must be central, it seems reasonable to impute it to certain motor innervations which condition the shifting of the mental attitude and may be incipient merely, but which, if completed, result in the shifting of the eyes and the changes of bodily attitude which accompany the scrutiny of an external object. And the sensory process is, to some extent at least, conditioned by the motor, if, indeed, the two are anything more than different aspects of one and the same process.[7]
But where, now, the subject is occupied in mentally tracing the boundaries of one of his two images he must inhibit all motor innervations incompatible with the innervations which condition such tracing: the rival process must cease, and the rival image will fade. He may, it is true, include both images in the same mental sweep. The boundary line is not the only possible line of movement. In fact, we may regard this more comprehensive glance as equivalent to an enlargement of the boundaries so as to include different mental objects, instead of different parts of but one. Or, since the delimitation of our 'objects' varies with our attitude or aim, we may call it an enlargement of the object. But in any case the mental tracing of a particular boundary or particular spatial dimensions seems to condition the sense of the corresponding content, and through inhibition of inconsistent movements to inhibit the sense of a different content. No measure of the span of consciousness can, of course, be found in these reports. The movements of the attention are subtle and swift, and there was nothing in the form of the experiments to determine at any precise instant its actual scope. All we need assume, therefore, when the images are said to be seen together, is that neither has, for the time being, any advantage over the other in drawing attention to itself. If in the complete observation, however, any such advantage appears, we may treat it as a case of inhibition. By definition, an idea which assumes a place in consciousness which but for itself, as experiment indicates, another might occupy, inhibits the other.
Fig. 3.