SIMULTANEOUS CONTRAST OR SPATIAL INDUCTION 129 



previous stimulation of the eye (Hering, Hess 1 , Tschermak) and fatigue 

 (Tschermak and Krause). The discrepancy between the induced and 

 the complementary colour is said to be absent when the eye is dark- 

 adapted (Mayer, Kuhnt 2 ). There are also psychological factors, which 

 form at any rate the most probable explanation of simultaneous con- 

 trast over colour-scotomatous areas (Tschermak 3 ) and over the blind 

 spot. The entoptic visibility of the blind spot 4 is itself evidence of 

 contrast, as are also the effects of stimulation of the optic nerve by 

 the constant current (G. E. Miiller 5 ). 



Simultaneous contrast is under ordinary conditions limited to the 

 eye stimulated (Hering 6 ), but binocular contrast can also be proved to 

 occur 7 . 



1 Arch.f. Ophth. xxxv. 4, 1, 1889 ; xxxvi. 1, 1, 1890. 



2 Loc. cit. xxvn. 3, 1, 1881. 



3 Arch.f. d. ges. Physiol. LXXXII. 559, 1900. 



4 Brewster; Purkinje; Aubert; v. Helmholtz ; Charpenfcier, Compt. rend, cxxvi. 1(534, 

 1898. 



- 5 Ztsch. f. Psychol. u. Physiol. d. Sinnesorg. xiv. 329, 1897. 



fi Loc. cit. i. 18, 1890. 



7 Fechner ; H. Meyer ; v. Helmholtz ; Hering, in Hermann's Handb. d. Physiol. in. 

 i, (iOO, 1879 ; Ebbinghaus, Arch.f. d. yes. Physiol. XLVI. 498, 1894 ; Chauveau, Compt. rcurl. 

 cxin. 1891 ; D. Axenfeld, Arch. ital. de Biol. xn. 28, 1889 ; xxvu. 103, 1897 ; Burch, Jl. of 

 Physiol. xxv. 1900. 



p. c. v. 



