INDIVIDUAL DIFFERENCES 39 



"1 1" 



changed to 1 in the interference test, and this particular per- 

 formance persisted nearly a month later in the retention period. 



It has been noted from the careful study of each animal's be- 

 havior, that individual errors, or tendencies to make such errors, are, 

 as a rule, gradually overcome, that a wrong movement made in the 

 first few trials persists throughout several succeeding trials in a 

 gradually diminishing extent. One mouse persisted in turning once 

 to the left gate in the first compartment, when the gates were opened 

 on the right side. It continued to do this for several days, when it 

 was noted that it began to go only part way to the left gate; then 

 turning around it took the successful path. This mouse never com- 

 pletely broke the habit, but in the end, the turn to the left had de- 

 generated into a quick whirl around in a circle, followed by a dash 

 through the proper gates. This type of behavior has been noted by 

 other observers; the following is quoted from page 32 of Basset's 

 monograph: 3 "As in the maze experiment, many of the inbred rats 

 were subject to errors which persisted throughout the experiment. 

 In particular may be mentioned one rat that invariably formed a 

 loop in the course from the entrance to the point of operation." 



Fig. 7 gives the daily record for mouse No. 134, Agouti $, whose 

 average time records are given in Table VI. This record shows an 

 initial set of seventeen trials in the maze test that almost duplicates 

 the theoretical learning curve. The daily record for eight days, 

 from the .tenth trial to the eighteenth, which marked the application 

 of the interference test, shows that the animal approximated the 

 physiological limit of performance; taking an average time of one 

 second per trial and making no errors at all during that period. The 

 interference effect for the animal is slight, as shown by the first 

 group of two trials, the remaining ten trials of the interference are 

 a little irregular, but the noticeable individual difference in the be- 

 havior of this mouse is to be seen from the very poor record it made 

 in the multiple choice test. It did not make a successful trip in 

 that test until the sixth day and then failed for eleven consecutive 

 days, from the eighth to the eighteenth day, inclusive, and also failed 

 on the twenty-second day. During all these trials the animal ap- 

 peared to be in very good health, it was active in the apparatus as 

 well as in its nest box and made plenty of errors in testing the col- 

 ored doors. It is tempting to speculate that the poor records of this 

 mouse in the multiple choice test were due to an interference effect 

 carried over from the previous training in the maze, but perhaps the 

 relatively poor retention test that followed would seem to disprove 





