SIZE AND FORM PERCEPTION 91 



o 28+ — o 19+, having only three right choices, was even more 

 negative, but when the o 28+ — o 15+ discrimination was tested, 

 the results were clearly positive. The standard was chosen 

 nine times and the variable was chosen only once. Here is 

 probably the place where, in the earlier training, the new cue 

 first figured. While the average results of the tests with the 

 G 19+ variable are slightly in favor of the larger stimulus, I 

 believe the fact should not be emphasized, for the larger circle 

 was chosen in 60 trials only five more times than would have 

 occurred had chance alone determined the choices. 



Table 3 summarizes the results of my investigation on the 

 chick's perception of size. In some cases the results are not 

 so clear cut as one might wish, but this fact is due to the uncer- 

 tainty of health among the birds which made it advisable to 

 hurry the tests, without waiting in some cases for the acquisi- 

 tion of perfect habits, in order to take the chicks to their limit 

 in discrimination. 



By considering not only the right-wrong records but also the 

 peculiarities in behavior which cannot be presented in tabular 

 form, I am convinced that the largest variable the chick can 

 distinguish, under the conditions here described, from a stan- 

 dard o 28+ lies somewhat above 15+. The quantitative 

 measurements on the basis of right choices points strongly to 

 this conclusion. Every subject, excepting 7 and 20, succeeded 

 in making at least 88% of correct choices in a series when the 

 O 28+ — o 15+ discrimination was required. Even in the case 

 of the two exceptions, 7 and 20, an efficiency of 70% was ac- 

 quired. But more convincing still is the fact that two chicks, 

 3 and 17, reached 90%, and two, 16 and 21, made perfect series. 



The time used in choosing is a factor which offers a means of 

 measuring quantitatively the chick's threshold of discrimina- 

 tion. It should not be unduly emphasized for it is not wholly 

 reliable, yet in these experiments it tends to substantiate the 

 conclusion which has been based upon the percentage of right 

 choices. Since the animal is less acquainted with the condi- 

 tions during the o 28+ — o 7+ discrimination as compared with 

 the o 28+ — o 15+ discrimination, it would be expected, other 

 things remaining constant, to choose more readily during the 

 later tests. Furthermore, the increase in age and activity 

 should enable it to choose more rapidly during the later tests. 



