110 HAROLD C. BINGHAM 



actually depended upon form difference. If it had a perception 

 of form such as has been found to exist for size, then no marked 

 change in the results should have occurred when o 28+ was 

 replaced by a circle that circumscribed or; inscribed the standard 

 triangle ; and if the chick perceived three-sidedness or triangu 

 larity on the one hand and circularity on the other hand, there 

 should have been no important modification of ito reaction when 

 the triangle was inverted. 



The work on form thus indicated that the chick can discrim- 

 inate between circles and triangles of equal area, and there are 

 indications of a discrimination between circles and squares of 

 equal area (witness series 21, April 25, table 9, and series 23, 

 March 16, table 7), but with the application of control tests we 

 have indications that this discrimination is on some basis other 

 than form. The results from the inversion of the triangle indi- 

 cate that the basis of choice depends upon the unequal stimu- 

 lation of different parts of the retina. When the extended base 

 of the triangle is so placed as to stimulate the region of the 

 retina which was formerly stimulated by the apex of the tri- 

 angle, the chick becomes confused. Under the conditions of the 

 present experiment, therefore, I am forced to conclude that the 

 apparent reactions to forms are the result of keen perception of 

 size differences. 

 • 



V. RELATIVE VALUE OF SIZE, FORM, AND BRIGHTNESS 



The preceding study of size and form can leave no doubt as 

 to their relative importance in the chick's visual life. On the 

 basis of trial and error it has been shown that the number of 

 tests to produce any approach towards a perfect response to 

 the circle-triangle is vastly greater than the necessary number 

 in the case of the large-small discrimination. This study has 

 also revealed the fact that even after perfect reactions to the 

 circle-triangle were established, the form element played no part 

 in the discrimination. The size element, under these conditions, 

 is the important factor for the chick, and form in the stricter 

 sense has been found to have no discriminative value. 



A brief study was made to determine experimentally the 

 relative importance of size, form, brightness, and general illu- 

 mination. The subjects used were Nos. 15, 16, 17, 18, 20, and 

 21. They were trained to go to a triangle which had a greater 



