THE PERCEPTION OF SPACE. (IV.)

519 so, with most people, if they steadily look at one point of it with an unmoving eye ; and the same is the case with many other illusions. Now all these facts taken together seem to show vaguely it is true, but certainly that present excitements and after- effects of former excitements may alter the result of processes occurring simultaneously at a distance from them in the retina or other portions of the apparatus for optical sensation. In the cases last considered, the moving eye, as it sweeps the fovea over certain parts of the figure, seems thereby to determine a modification in the feeling which the other parts confer, which modification is the figure's ' distor- tion '. It is true that this statement explains nothing. It only keeps the cases to which it applies from being explained spuriously. The spurious account of these il- lusions is that they are intellectual, not sensational. The distorted figure is said to be one which the mind is led to imagine, by falsely drawing an unconscious inference from certain premisses of which it is not distinctly aware. And the imagined figure is supposed to be strong enough to suppress the perception of whatever real sensations there may be. But Helmholtz, Wundt, Delboeuf, Zollner, and all the advocates of unconscious inference are at variance with each other when it comes to the question what these uncon- scious premisses and inferences may be. Fig. 12