34 HAROLD C. BINGHAM 



wrong stimulus was presented. The chick was allowed to go 

 alternately to each nest box 10 times. It was thus made fa- 

 miliar with the nest boxes and the reaction box. 



By displaying, always on the side of escape, the stimulus 

 which the chick was later to be trained to choose, the subject 

 was occasionally aided, prior to training, in acquiring a perfect 

 habit. ^ This fact was especially noticeable in the experiments 

 on size discrimination in which a circle 6 cm. in diameter always 

 appeared in that electric compartment by way of which the 

 subject escaped. At the end of the preliminary series a few 



chicks were responding perfectly to this condition of o 28 H 



o 7 + discrimination. 2 This perfect o 28 H o 7 + habit, 



however, may not mean that size was the basis of choice. It is 

 quite probable that the chicks chose the lighter compartment. 

 Precaution was taken to eliminate this possibility before size 

 tests were completed, and control tests were introduced to make 

 certain that it had been eliminated. 



This preliminary work was followed by the training series. 

 Both entrances to the nest boxes were now closed, and the only 

 cues that remained to aid the chick in reaching the nest box 

 were the two visual stimuli. Continuing with the example of 

 size discrimination, o 28 + was the positive sign, ©7+ was the 

 negative sign of escape from the experiment box. If a chick 

 chose o 7+ by stepping into that compartment, it was shocked 

 by momentarily closing the key, Z of figure 3. A single shock 

 was usually administered but if it were not effective it was re- 

 peated. The wet floors of A and B regulated the intensity of 

 the shock. Care in the manipulation of the shock was impor- 

 tant for it was essential that it be an effective punishment yet 

 mild enough to avoid frightening the animal. The results of 

 weeks of work could be destroyed in a moment through a 

 blunder in the method of punishment. 



In the early stages of training the chicks often went beyond 

 the exit towards the stimulus at the end of the compartment. 

 If the animal were allowed to do this it spent considerable time 

 and energy around this illuminated stimulus. By placing a 



^ A habit is termed perfect when a chick successively fnakes 20 correct choices. 



2 The stimulus demanding a positive response is named first followed by the 

 stunulus demanding a negative reaction. The dimensions represent the number 

 of square centimeters in the area. 



