REACTIONS OF CHICKS TO OPTICAL STIMULI 



FREDERICK S. BREED 



The University of Michigan 

 From the Harvard Psychological Laboratory 



One figure 



In the course of a previous study, 1 in which the rapidity of 

 development, permanency, and interrelation of certain habits 

 in barred Plymouth Rock chicks were tested, the problem sug- 

 gested itself of determining more accurately the nature of some 

 of the optical stimuli in response to which a chick is able to 

 acquire a habit of reaction. In these earlier experiments the 

 animals were tested in their ability to discriminate two simul- 

 taneously presented stimuli differing essentially in color, form, 

 or size. Although certain conclusions as to the what of discrim- 

 ination seemed quite safe, it was thought best to conduct a 

 further investigation in this direction with greater refinement of 

 method. The earlier tests seemed to yield positive results in 

 the discrimination of color and size differences, and negative 

 results in the tests on forms. 



The problem, then, became that of determining more accu- 

 rately whether or not the elements of form, size, and color may 

 become the basis of discrimination for the chick. The work 

 was undertaken and completed in the Harvard Psychological 

 Laboratory under the guidance of Professor Robert M. Yerkes, 

 who proposed the investigation and assisted throughout with 

 invaluable suggestions. 



APPARATUS 



A perspective of the apparatus employed is shown in 

 figure i. For a complete description, including dimensions of 

 parts, the reader is referred to an article by L. W. Cole in an 

 earlier number of this journal. 2 Following Cole's description, 

 we may consider the apparatus as composed of three boxes: 

 (i) The hover box, O; (2) the illumination box, covered by the 



1 Breed, F. S. The development of certain instincts and habits in chicks- 

 Behavior Monographs, vol. 1, no. 1, 1911, p. 41 ff. 



2 Cole, L. W. The relation of strength of stimulus to rate of learning in the 

 chick. The Journal of Animal Behavior, vol. 1, no. 2, 1911, p. 112 ff. 



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