VISUAL PERCEPTION OF THE CHICK 11 



Was the third dimension constant? These are some of the 

 factors which must be known before one can safely say that the 

 chick perceives form. One could truthfully state that an ani- 

 mal discriminates between a circle and a triangle if it regularly 

 chooses the former even though the triangle be twice as large 

 as the circle, but it is improbable that the basis of discrimina- 

 tion in such a case would be anything other than size. Since 

 such points are ignored in the report by Katz and Revesz, one 

 suspects of the experimenters carelessness in technique. 



Furthermore, no information is offered as to the method of 

 cutting these forms. It is a difficult matter to cut green peas 

 with regularity. Can we be certain that the chicks discrimi- 

 nated on the basis of form rather than irregularity of surface? 

 No mention is made of controls to eliminate this possibility. 

 Because the authors leave vital points like these unmentioned 

 and apparently unnoticed, one is inclined to regard the experi- 

 ment as quite superficial. 



A definite answer to the controversy of the semi-experimental 

 school over the nature of the chick's instinctive reactions is 

 offered for the first time by Breed (4).^ His study of the in- 

 stincts is supplemented by his study of certain habits, out of 

 which grew the problem of accurately determining the nature 

 of the color, form, and size stimuli in response to which a chick 

 is able to acquire a habit of reaction (5). The chief significance 

 of Breed's later study appears in his contribution to the de- 

 velopment of the dark-room method. For testing the chick's 

 perception of colors. Breed combines the Yerkes discrimination 

 method (34) with the Hess (9-11) dark-room method. The 

 next step is the adaptation of the combined methods to investi- 

 gations of size and form perception. The stimuli were presented 

 to the chicks by means of the illumination of two plates of opal 

 flashed glass over which were set mats of tin or cardboard con- 

 taining the desired openings. Thus the chick was given an 

 opportunity of selecting a circle when appearing with a square, 

 or of discriminating a larger from a smaller stimulus. 



^Certain instincts have later been carefully observed by Pearl (24). The 

 instincts considered relate primarily to behavior having practical significance 

 for the poultry keeper. In the single reference cited at the close of this chapter, 

 there appears a selected bibliography referring to a number of other papers on 

 related subjects. 



