244 PSYCHO LOOT. 



a mirror's surface continues to be seen beJiind the mirror, althougb we 

 know that to all tliese appeaiances no outward reality corresponds. 

 True enough, we can remove our attention, and keep it removed, from 

 sensations that have no reference to the outer world, those, e.g., of the 

 weaker after-images, and of eutoptic objects, etc. . . . But what would 

 become of our perceptions at all if we had the power not only of ignor- 

 ing, but of transforming into their opposites, any part of them that 

 differed from that outward experience, the image of which, as that of 

 a present reality, accompanies them in the mind ? " * 



And again : 



" On the analogy of all other experience, we should expect that the 

 conquei'ed feelings would persist to our perception, even if only in the 

 shape of recognized illusions. But this is not the case. One does not 

 see how the assumption of originally spatial sensations can explain our 

 optical cognitions, when in the last resort those who believe in these 

 very sensations find themselves obliged to assume that they are over- 

 come by our better judgment, based on experience." 



These words, coming from such a quarter, necessarily 

 carry great weight. But the authority even of a Helmholtz 

 ought not to shake one's critical composure. And the mo- 

 ment one abandons abstract generalities and comes to close 

 quarters with the particulars, I think one easily sees that 

 no such conclusions as those we have quoted follow from 

 the latter. But profitably to conduct the discussion ive 

 must divide the alleged iTistances into groups. 



(a) With Helmholtz, color-perception is equally with space- 

 perception an intellectual affair. The so-called simulta- 

 neous color-contrast, by Avhicli one color modifies another 

 alongside of which it is said, is explained by him as an 

 unconscious inference. In Chapter XVII we discussed the 

 color-contrast problem ; the principles which applied to its 

 solution will prove also applicable to part of the present 

 problem. In my opinion, Hering has definitively proved 

 that, when one color is laid beside another, it modifies the 

 sensation of the latter, not by virtue of any mere mental 

 suggestion, as Helmholtz would have it, but by actually 

 exciting a new nerve -process, to which the modified feeling 

 of color immediately corresponds. The explanation is 

 physiological, not psychological. The transformation of 



* Physiol. Optik, p. 817. 



