372 HARVEY CARR 



mastery of the problem. It must certainly be detrimental in 

 part because this habit must be broken before the problem can 

 be mastered. The detrimental character of the habit is evident 

 from the following facts. Each animal was ranked as to speed 

 of learning. The three rats that developed no preference stood 

 1st, 2nd, and 6th in quickness of mastery. Among the five rats 

 with a position preference those two which first eliminated this 

 tendency were also the first to master the problem, while that 

 animal which was the last to eliminate the tendency was also 

 the last to complete the mastery of the problem. 



The existence of these position preferences explains the rela- 

 tive speed of development of the two habits as previously de- 

 scribed and illustrated in figures 5 and 6. The group of five 

 animals that developed a preference for the left position con- 

 tained the same individuals as the group that exhibited the 

 greater progress in the mastery of the left path. The three 

 animals that developed no position preference were the ones 

 which mastered the two habits simultaneously. The distribu- 

 tion of the total choices between the two exits was practically 

 identical with the distribution of the correct choices alone; this 

 relation holds for the records of the group and each of the indi- 

 viduals. No matter how the total number of entrances are 

 distributed between the R and L exits, the percentages of cor- 

 rectness for each are practically the same. In case a rat chooses 

 the left exit 80 times in a series of 100 trials when it has devel- 

 oped an accuracy of 75%, the numbers of correct choices for 

 the left and the right exits will be 60 and 15 respectively. The 

 absence of a position preference will give 50 entrances for each 

 of the exits in a series of 100 trials, and in this case the number 

 of correct and successful responses will be equally distributed 

 between the two paths. Since the percentage of successful 

 responses is independent of the distribution of the choices, the 

 number of correct choices of either exit must be a function of 

 the frequency with which it is entered. In other words, the 

 relative progression in the mastery of the two habits as illus- 

 trated in figures 5 and 6 is almost wholly a function of the posi- 

 tion preferences which have been developed. 



The rats may repeat or alternate from the previous choice 

 and this alternation may or may not conform to the objective 

 sequence. An analysis of the results reveals the following 



