AD APT A TION AND IND UCTION. 



1065 



This mode of psychological explanation has been criticised by Hering, 

 and its application to these phenomena shown conclusively, by means of varia- 

 tions of the experiments, to be unwarranted. 1 In the case of all, the contrast 

 colour may, by suitable means, be made so intense, that observers, unaware of 

 the nature of the experiment, may not know which is the objective and which 

 the subjective colour. In the case of Meyer's experiment, the fact that the 

 grey patch in front of the cover is so little affected by contrast, is due to the 

 effect of differences of texture, etc., obscuring the colour difference. Hering 

 found that if the grey patch was carefully covered with tissue paper, so that 

 it exactly resembled the other patch, both showed the contrast colour equally 

 well. Another argument used by Helmholtz was, that a black line marking 

 off the patch from the surrounding area, much diminished the contrast colour ; 



FIG. 385. The shaded rings represent the coloured portions of the 

 disc. The other rings give on rotation a grey of medium 

 brightness which is coloured by contrast. 



but this is to be expected if, as generally acknowledged, contrast colour is most 

 marked immediately adjoining the inducing surface. In the case of mirror 

 contrast, Hering has devised a form of the experiment in which observers may 

 see the most pronounced contrast effects, while wholly unaware that they are 

 looking through a coloured medium. 



Hering has shown that Helmholtz's results with the coloured shadow are 

 due to the lack of careful fixation, and to the effect of successive contrast. 

 After steady fixation through a tube of the line of junction of the illuminated 

 surface and blue shadow, the after-image is seen on removing into the shadow, 

 or on extinguishing the yellow light, the blue colour showing in the half 

 previously illuminated, while the half previously rendered blue by contrast 

 becomes colourless, or may even be tinged yellow. On removal of the tube, or 

 better, on opening the tube so as not to disturb fixation, the after-image is 

 still seen on the larger background. 



Hering 2 has devised a binocular experiment which conclusively disproves 



1 Arch. /. d. gcs. Physiol., Bonn, 1887, Bd. xl. S. 172 ; and Bd. xli. S. 1 and 358. 



2 Ztschr. f. PsychoL u. Physiol. d. Sinnesorg., Hamburg u. Leipzig, 1890, Bd. i. S. 18. 



