si i HAROLD C. BINGHAM 



box "ii that side where the right stimulus appeared was open; 

 the sliding door closed the entrance from the electric box where 

 the wrong stimulus was presented. The chick was allowed to 

 go now to one, now to the other nest box, in irregular sequence 

 until it had found its way 10 times to each. It was thus made 

 familiar with nest boxes and the experiment box. 



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

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

 was occasionally aided in acquiring a perfect habit. 6 This 

 condition was especially noticeable in the experiments on size 

 discrimination. In this case a circle 6 cm. in diameter always, 

 appeared in that electric compartment from which the subject 

 « scaped. At the end of the preliminary series a few chicks had 

 acquired a perfect response to this condition of o 28+ — o 7+ 

 discrimination. 7 This perfect o 28+ — o 7+ habit, however, may 

 not mean that size was the basis of choice. It is quite possible 

 that the birds chose the lighter compartment. Precaution was 

 always taken to eliminate this possibility before size tests were 

 completed, and control tests were carefully planned 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 to reach the nest box 

 were the two optical stimuli. Continuing the example of size 

 discrimination, :i 28+ was the positive sign, o 7+ was the nega- 

 tive sign of escape from the experiment box. At this point in 

 the training the electric shock was introduced. If a chick chose 



7+, i.e., stepped upon the wires of that compartment, it was 

 shocked. This was done by momentarily closing the key, Z, 

 (figure 1). A single shock was usually given, but if the be- 

 havior of the bird indicated that the shock had not been sensed, 

 it was repeated. The wet floors of A and B served to regulate 

 the intensity of the shock. Great care was necessary to provide 

 a shock that was an effective punishment yet not severe enough 

 to frighten the animal. Care in the manipulation of the shock 

 was also essential. The results of weeks of work could be 

 destroyed in a moment through an error in the administration 

 punishment. 



A habil is termed perfect when a chick successively makes 20 correct choices. 

 'The stimulus demanding a positive response is named first; following this is 

 the stimulus demanding a negative reaction. 



