COLOR VISION IN BIRDS 499 



as for ourselves. Revesz, in 1921, trained birds to peck rice from pieces of 

 green paper on large gray backgrounds. He then offered them rice on 

 both green-on-gray and gray-on-red combinations. The birds took food 

 from both, showing the 'induction' of greenishness, in the gray, by the 

 surround of complementary red. When offered gray-on-gray, or gray on 

 colors other than red, they were negative. By a similar procedure, blue- 

 yellow contrast phenomena were also elicited. 



Few species other than the convenient domestic fowl have been studied 

 to any great extent. Hamilton and Coleman investigated the hue-discrim- 

 ination curve of the pigeon in 1933. They used a procedure quite differ- 

 ent from Lashley's, altering the wavelength of the positive stimulus, by 

 lOmfJ, steps, toward that of the negative stimulus. The wavelengths near 

 which small differences in hue were best appreciated proved to be 580m|l 

 and 500m[X — values not far from those for man (580m|i and 490m|x) . 

 The indications were that in the pigeon the 'green-ness' process (p. 

 94) does not commence until ?L620m[j, is reached, instead of at 650m[X 

 as in man; and at X530m[A the violet-ness process takes complete charge. 

 The pigeon also seemed less sensitive to changes in wavelength than man, 

 though, unlike the fish, it pays much more careful attention to hues than 

 to brightnesses. Where man distinguishes 160 spectral segments, the 

 pigeon can discriminate only 20 between ?u700m|j, and A,460m[i; but of 

 course the bird's real capacity in this regard is concealed, in any training 

 technique, by its low intelligence. When a human observer is put under 

 instrumental handicaps similar to those of Hamilton and Coleman's 

 pigeons, he may be able to distinguish no more than 20 or 30 hues, as 

 Edridge-Green found. The pigeon was actually able to make discrimin- 

 ations where its human overlords could not; and probably, through the 

 instrumentality of the oil-droplet mosaic, it really has many more hue- 

 experiences than we can possibly help it to demonstrate to us (see p. 502) . 



The activities of birds are guided almost entirely by vision, but they 

 are the stereotyped actions of an essentially stupid group of creatures. 

 The most intelligent of all birds are probably the parrots and their near 

 allies. The color vision of one of these, the budgerigar or Australian 

 zebra grass-parakeet (Melopsittacus undulatus) , was investigated by 

 Bailey and Riley in 1931, and independently by Plath in 1935. Bailey 

 and Riley were primarily interested in the budgerigar's ability to form 

 and break psychological associations with colors. Their study of its color 

 vision as such, while technically much more elaborate than Plath's, was 

 beclouded by misconceptions of the nature of hue and saturation. Plath's 



