SIZE AND FORM PERCEPTION 111 



area and was brighter than the simultaneously presented circle. 

 The triangle also appeared in the compartment which was more 

 highly illuminated than that in which the circle was presented. 

 After the chick had learned to choose the triangle without any 

 errors, all but one of these factors were eliminated. It was thus 

 determined which factor had the greatest value for the chick. 



This method, I clearly recognize, is not reliable. It was only 

 adopted as a means of securing preliminary information on this 

 particular problem. The most important defect which may be 

 present is that it provides no certain way of ascertaining the 

 threshold values for each visual factor. For example, a differ- 

 ence of ii sq. cm. between the areas of the two stimuli may be 

 high above the chick's threshold of difference, whereas the differ- 

 ence between a triangle and a circle may be scarcely above this 

 liminal threshold. I had no way of equalizing the four factors 

 for discrimination. Subsequent work such as that reported on 

 size and form must determine these values for all of the "light" 

 elements on the basis of right and wrong choices. 



The amount of difference in brightness and general illumina- 

 tion was that which, under the mechanical conditions previously 

 described, would result when the right source lamp was placed 

 125 cm. from its stimulus area and the wrong lamp was 240 cm. 

 from its display surface. This caused a marked difference to 

 the human eye both in brightness and general illumination. 

 Table 10, however, shows that it was of little significance to the 

 chick. According to the averages, size was the first factor; 

 right choices depending upon it alone amounted to 86%. Bright- 

 ness and general illumination combined stand next with nearly 

 70% of right choices, and form stands last with the right and 

 wrong choices nearly equal. Considering these results in con- 

 nection with those previuosly presented on size and form, it 

 seems highly evident that the relative values of light factors for 

 the chick's vision is respectively size, brightness and general illu- 

 mination, and form. 



VI. GENERAL IDEA 



The frequent recurrence of discussions relative to the general 

 idea in connection with animal studies has had the effect of 

 keeping before me, during the present study, the question 

 whether or not the chick has a general idea of sizes and forms. 

 Accordingly, after several subjects had been trained to make 



