22 JOSEPH U. YARBROUGH 



ber 39 was very slow in beginning the transfer, but when once 

 started the percentage increased normally. 



The gradual growth of the association in this group is obvious 

 from the curve in Fig. 4. Each point of this curve represents 

 the average for the group in percentage of correct response for 

 20 trials of the regular learning series. Although we had used 

 the 30 per cent of undisturbed trials throughout these experi- 

 ments, at the end of the work each animal was given a special 

 series of ten test trials in which pain was withheld. In these tests 

 the response was unaffected. The group required an average of 

 229 trials to reach the standard imposed. 



4) Four-second Interval. With Group V the sound was pre- 

 sented four seconds before pain. Seven animals were used in 

 the group, and Table V gives their data. There are no marked 

 individual differences, a gradual increase in correct responses 

 being maintained by each animal, as is graphically shown in the 

 learning curve in Fig. 5. 



TABLE V 



Animal Trials % on Last 100 



4 236 94 



13 265 92 



1 6 240 91 



19 187 91 



40 228 93 



41 216 94 

 52 269 91 



Average 236 92.4 



After the work was completed the special set of test trials was 

 given with no effect upon the per cent of correct responses. The 

 average number of trials necessary for mastery was 236. 



5) Six-second Interval. Group VI made the association over 

 an interval of six seconds. Table VI shows the number of trials 

 necessary to make the association and the standard of correct 

 reaction reached. From the table and the learning curve in Fig. 

 5 it is possible to appreciate the general disturbance during the 

 first 60 to 100 trials, as well as the gradual growth of the asso- 

 ciation. During this first period of learning the animals not only 



