136 



COLOUR VISION 



The conclusions which Kalischer draws from his experiments are as 

 follow : 



(a) That there is no doubt of the ability of dogs to perceive 

 differences of hue as well as differences of brightness. 



{b) That whereas such colour discrimination is cortical, brightness 

 discrimination is to some extent sub-cortical, reactions to changes of 

 illumination being found to occur even after extirpation of the visual 

 cortex. 



(c) That there exist considerable individual differences in the sensi- 

 bility of dogs to colours. 



By far the most exhaustive experiments on dogs have been carried 

 out bv Miss E. M. Smith^. The apparatus used is shown in Figs. 42 and 



o 

 o 



r-t 



u 



trial-box 



o 

 o 



^ ■window-door ^ 



Fig. 42. Ground plan of experimental dog box. (E. M. Smith.) 



43. It will be noticed that the " home box " is separated from the 

 " trial box " by a partition in which there are five glass screens Sj.^. 

 Cards of various colours could be introduced into these screens. The 

 dog was placed in the home box and let into the trial box through Sj, 

 which was then closed. The preliminary " general training " con- 

 sisted first in teaching the dog to pass through the screens. These 



1 Brit. Jl. of Psychol, v. 119, 1912. 



