THE COLOR VISION OF BIRDS 



13 



TABLE 1 



Tests for red-green discrimination with varied brightness relations of the stimulus 

 lights. The energies at which the red was known to be brighter are printed in 

 italics. In the remaining tests the brightness value of the green was equal to or 

 greater than that of the red. Energies are expressed in decimals of the Pfund 

 standard. 



Chick A 

 (Positive to red) 



Chick C 

 {Positive to green) 



TABLE 2 



Tests for Red-Green Discrimination with Varied Saturation 

 of the Stimulus Lights 



Condition of stimuli 



Chick A 



No. of 

 trials 



No. of 

 errors 



Chick C 



No. of 

 trials 



No. of 

 errors 



Both lights at standard energy 



Green much diluted 



Bright white light substituted for green 



Both lights at standard energy 



Red much diluted 



Red diluted until its quality was lost . . . 



Both lights at standard energy 



White light of low intensity for red .... 



Same white for green 



White light of high intensity for red . . . 



Same white for green 



Both lights at standard energy 



Two white lights of equal brightness . . . 



5 

 10 



5 

 10 

 10 



7 



5 



8 

 10 



5 

 10 



5 

 10 







1 



3 

 

 

 4 

 

 

 1 

 

 3 

 

 5 



5 



6 

 5 



5 

 10 



5 

 12 

 6 

 6 

 5 

 6 

 10 





 

 1 

 1 

 4 



'o 



4 

 

 3 

 

 

 2* 



* A careful examination was made for secondary criteria which might account 

 for this choice which tends to invalidate all the results obtained with Chick C. 

 Nothing could be discovered by the dark adapted human eye. The test was re- 

 peated on the following day, when ten trials with five errors were obtained. The 

 above record was probably a chance variation. 



