SIZE AND FORM PERCEPTION 79 



ually to eliminate the inequalities which were not wanted, 

 until only the visual factor in question remained. 



j. Method and technique 



These changes in the problem are closely allied with the 

 mode of procedure. The mechanical phase of my method 

 appears in the description of the apparatus, but it does not 

 fully explain the application of this procedure to the study 

 of the chick's visual perception. This topic might well be con- 

 sidered in two parts: — the one dealing with the mechanism, 

 the objective aspect, and the other relating to the plan of pro- 

 cedure, the personal aspect or technique. In this report I shall 

 not attempt to make such a sharp distinction, for while the 

 two topics are, in many respects, clearly distinct, I find them 

 so closely interrelated that it is impracticable to consider them 

 separately. In general, however, I shall devote the first part 

 of this section primarily to method, and in the latter part, 

 the discussion will be continued more from the standpoint of 

 technique. 



The plan of the apparatus in relation to the chick is to pro- 

 vide conditions both desirable and undesirable. Either nest 

 box includes those factors which the chick wants. It provides 

 food, light, warmth and companionship. The experiment box 

 is arranged to make the chick want to get out. In the entrance 

 box the chick is closely confined; in both the entrance and 

 discrimination chambers the floors are wet ; the entire experi- 

 ment box, exclusive of the nest boxes, provides faint illumina- 

 tion, little warmth, no food and no companionship. When a 

 chick, familiar with the nest boxes, is placed in the entrance 

 box its natural desire is to get back to one of the nest boxes. 

 Its problem, then, is to learn how to get to the desirable part 

 of the apparatus. 



The two visual stimuli which are displayed on the stimulus 

 shifter indicate to the animal which nest box to choose. Dur- 

 ing the training series, both electric compartments are identical 

 except for the difference between the two stimulus areas. Since 

 the animal wants to reach the nest box it will try to find a way 

 of accomplishing this end. 



Each chick was taught the way of escape to the nest box 

 by means of 20 preliminary trials. The entrance to the nest 



