RATE OF LEARNING IN THE WHITE RAT 25 



introduce another stimulus affecting still another sense at certain 

 definite time intervals before the buzzer, just as the buzzer had 

 been entered before pain in the groups previously reported. 

 Light was selected for this new stimulus. By properly connect- 

 ing the timing apparatus in the light circuit as described above, 

 it was possible to present the two stimuli (sound and light) with 

 a known time interval between them. The animals were re- 

 grouped and five new groups were set to work on learning to 

 transfer their motor response from sound over to light. With 

 the exception of the time interval, conditions were constant for 

 all the groups. As before, experiments were made with con- 

 tinuous presentation and with one, two, four, and six second in- 

 tervals. The 90 per cent standard was again adopted. In all, 

 24 animals were used on this problem. 



i ) Continuous presentation. Here the problem was the asso- 

 ciation of light with sound when presented in immediate suc- 

 cession. The data for this group are given in Table VIII. One 



TABLE VIII 



Animal Trials 



48 100 



49 ioo 



50 ioo 



51 ioo 



Average ioo 91 . 5 



hundred trials were given to each animal, but the test trials show 

 that the association was complete at the end of 60 trials. The 

 curve in Fig. 6 shows a period of fluctuation in correct response 

 between the regular series and the test trials. After 60 trials in 

 the regular series the curve remains almost uniform at 90 and 

 above. This uniformity was reached in Group II at the end of 

 40 trials. A comparison of this curve with that of Group II, 

 Fig. 4, indicates that the light and the buzzer offered a problem 

 of practically equal difficulty with the sound-pain association in 

 the first part of the period, but the transfer to light was more 

 readily made. From a study of the individual records in the 

 two groups it was found that under these conditions when ani- 



