248 PSTCEOLOG Y. 



from Vierordt on page 188, and seems to take us back to a 

 primitive stage of perception, in which the discriminations 

 we now make when we feel a movement have not yet been 

 made. If we draw the point of a pencil through * ZoIIner's 

 pattern ' (Fig. 60, p. 232), and follow it with the eye, the 

 whole figure becomes the scene of the most singular 

 apparent unrest, of which Helmholtz has very carefully 

 noted the conditions. The illusion of ZoUner's figure van- 

 ishes entirely, or almost 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 shoio — vaguely 

 it is true, but certainly — tliat 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 ' distortion.' It is 

 true that this statement explains nothing. It only keeps 

 the cases to which it applies from being explained spuri- 

 ously. The spurious account of these illusions is that they are 

 intellectual, not sensational, that they are secondary, not primary, 

 mental facts. The distorted figure is said to be one which 

 the mind is led to imagine, by falsely drawing an uncon- 

 scious inference from certain premises 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, Wuudt, 

 Delboeuf, Zollner, and all the advocates of unconscious in- 

 ference are at variance with each other when it comes to 

 the question what these unconscious premises and infer- 

 ences may be. 



That small angles look proportionally larger than larger 

 ones is, in brief, the fundamental illusion to which almost all 

 authors would reduce the peculiarity of Fig. 67, as of Figs. 

 60, 61, 62 (pp. 232, 233). This peculiarity of small angles 

 is by Wundt treated as the case of a filled space seeming 

 larger than an empty one, as in Fig. 68 ; and this, according 



