THE COMPARATIVE PSYCHOLOGY OF COLOUR VISION 133 



each had a disc in front, l!5 cm. in diameter, of which two held grey 

 papers and one a saturated green. The "' green ' box contained a 

 biscuit. After training it was found that out of fifty papers, ranging 

 from black to white there was no grey which, when presented to the 

 subject for discrimination from the standard green, yielded a percentage 

 of errors greater than 31. Later tests showed that such discrimination 

 only occurred under certain conditions. If the grey was presented 

 as a square and the green as a circle, green was chosen : but if the green 

 was a triangle or square, the grey square was invariably chosen. Hence 

 the discrimination of a colour from a series of greys is only possible 

 when the conditions have been thoroughly learnt. 



Nicolai 1 , did not succeed in teaching his two dogs to distinguish 

 between red and green bowls. Colvin and Burford 2 experimented in 

 the same manner with three dogs, a cat, and a squirrel, food being 

 placed in red receptacles amongst similar empty receptacles of other 

 colours. The colour was distinguished in 87 '3 per cent, of trials, the 

 squirrel responding best. Kinnaman 3 attempted in a series of similar 

 feeding experiments to eliminate the ambiguity of discrimination of 

 brightness and colour-differences. Monkeys were tested with glass 

 tumblers covered with papers of different colours, and when it had been 

 shown that they were able to identify a vessel of a particular colour 

 as associated with food, the power of distinguishing the colour from 

 greys of the same brightness was tested. Kinnaman came to the 

 conclusion that the capacity to distinguish colours as such in monkeys 

 was undoubted. 



J. B. Watson 4 , criticising Kinnaman's results, says that the use of 

 coloured papers can never give a satisfactory test of colour vision in 

 animals. He himself used a spectrometer apparatus which illuminated 

 a screen with two monochromatic red and green patches. Food boxes 

 were placed beneath the patches, one being empty, the other containing 

 a grape. If the red box were opened the grape was obtained ; if the 

 green, the monkey was pulled back. In early tests with red and green 

 the animals failed to react to red. Blue-yellow discrimination arose 

 more rapidly than red-green in all cases (three monkeys). The experi- 

 ments were early vitiated by the onset of position habits. 



Yerkes 5 made very exhaustive experiments on the Japanese dancing 



1 .//./. Psychol. u. N enrol x. 1907. 



2 Psychol. Rev., Psychol. Monographs, xi. 1, 190!*. 



3 Amer. J. of Psychol. xm. 98, 173, 1902. 



4 ./. of Com /i. Xfitr. and Psychol. xix. 1. 1909. 



5 The Dancing Mouse, New York. 1902. 



