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.”

[Illustration:  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