JOSEPH U. YARB ROUGH 



100 



40 



100 



*Q| 



60 



40 



TrUls 80 



140 

 Figure 4 



220 



Trial* 



.120 



180 



240 



300 



Figure 5 



Curves 2, 3 and 4 (Fig. 4) are the learning curves for the Groups II, 

 III and IV, respectively. Curves 4, 5 and 6 (Fig. 5) are the learning curves 

 for Groups IV, V, and VI. 



is increased from two to four seconds. 4. The six-second inter- 

 val is more difficult than the four-second, but the increase in 

 difficulty is not so great as from the one-second to the two-second 

 interval. 



b) Association of Light with Sound.' When the animal had 

 made the association of sound with pain, the pain had in reality 

 dropped out, and the animal responded to the buzzer whenever 

 presented. To demonstrate the accuracy of this statement a 

 special set of test trials was given at the end of the learning 

 period in which pain was not given at all, and the percentage of 

 correct response was not affected. It was possible, therefore, to 



