98 HAROLD C. BINGHAM 



with a 3 cm. circle. Likewise, it can choose a 9 cm. circle 

 •circle when presented with a 6 cm. circle. In the one test, 

 what was formerly the sign for rejection is accepted as a positive 

 sign; in the other, what was the positive sign is rejected as the 

 -shock sign. Choices, it would thus seem, can be made on the 

 basis of relative stimulus difference. 



In the preceding paragraph, it has been said that the chick 

 €an choose on the basis of relative size difference. In my 

 preliminary account (Chapter II: 2, p. 113), the statement is 

 made that the chick will choose on this basis. Obviously, 

 my earlier assertion is too loose, for all chicks did not react 

 unmistakably in this manner. It would seem wholly safe, in 

 view of the number that did respond positively, to say that 

 the chick can react on the basis of size relationship. Whether 

 it will so respond probably depends somewhat upon the degree 

 of previous training. 



Coburn's investigation of the crow's reactions to relative 

 stimulus difference is hardly comparable with my work on the 

 chicks. Before the relative difference tests were made, the 

 crows had been trained with 5-2, 9-5, 5-3, 3-2, and 6-Z combi- 

 nations. On August 25th, the size training ended with the 

 6-3 combination. On the following day, "relative reactions" 

 to the 3-2 combination were tested with positive results. 

 This was followed by 6-4 training and positive results for the 

 "9-6 "relative reactions." Again the 6-4 training was followed 

 by positive results for the 3-2 "relative reactions." 



In comparison with the preliminary training of my chicks, 

 the crows had received a wide variety of experience with dif- 

 ferent circle combinations before the tests for relative reactions 

 were made. The crows had actually received training with 

 the 3-2 combination which makes me inclined to question the 

 propriety of Coburn's conclusion: 



The results of these experiments indicate fairly clearly the relativity of the 



crows' reactions For example, on August 24th and 25th, when the 



3 centimeter circle was presented with the 5 centimeter circle, the crow reacted 

 to the 3 centimeter circle thirty-seven times negatively and three times posi- 

 tively. On August 26, the 3 centimeter circle, displayed with the 2 centimeter 

 circle, was reacted to positively in every case. 



Coburn seems to overlook the fact that this same crow had 

 been specifically trained on the 3-2 relation from August 12th 

 to 17th. 



