REWARD AND PUNISHMENT IN HABIT FORMATION 235 



5. As the difficultness of discrimination is increased the strength of 

 that stimulus which is most favorable to the acquisition to habit for- 

 mation approaches the threshold. This leads us to infer that an easily 

 acquired habit, that is one which does not demand difficult sense dis- 

 criminations or complex associations, may readily be formed under 

 strong stimulation, whereas a difficult habit may be acquired readily 

 only under relatively weak stimulation. 



Prof. Lawrence W. Cole repeated the above experiment on the 

 chick with the discriminatory conditions somewhat changed to 

 fit the needs of his subjects (2). His results led him to the fol- 

 lowing conclusion : 



In conclusion, it is evident that within the limits of the stimuli which 

 I used, the number of trials required by the chick to learn to choose con- 

 secutively the darker of the two unequally illuminated screens, when 

 discrimination is easy, decreases with an increase of stimulus. Under 

 medium difficulty of discrimination the above law holds true only for 

 the lower intensities of the stimuli which were used or, in other words, 

 the optimal stimulus recedes towards the threshold from 590 to 480 (6) . 

 The above law for the condition of easy discrimination holds true for 

 that of difficult discrimination if we consider only the record of the 

 chicks which succeeded in learning to make the discrimination. If, 

 however, we consider only the chicks which failed, the optimal stimulus 

 recedes once more to a point nearer the threshold of stimulation than in 

 case of medium discrimination. In other words, with difficult conditions 

 of discrimination, strong stimuli divided the chicks into two groups, 

 those which succeeded in learning to discriminate by reason of more 

 right choices at the beginning of the training series and consequently 

 fewer pain stimuli, and those which failed because of fewer right choices 

 and more pain stimuli in the earlier trials. So far as I determined the 

 sensitiveness of chicks, it may be said that on the average the more 

 sensitive chicks learn more rapidly both for strong and weak stimuli. 



Mildred A. Hogue and Ruth J. Stocking did some work in Johns 

 Hopkins Psychological Laboratory on the relative values of 

 punishment and reward as motives (4). Their subjects were a 

 mixed breed of black-and-white rats. The problem for the rats 

 was to learn to discriminate between two lights of different in- 

 tensity, always choosing the. one and avoiding the other. The 



