30 JOSEPH U. Y ARE ROUGH 



obtained in each of these five groups the following table was 

 constructed. From these data and the curves presented the fol- 



TABLE XIII 



Group Time Interval Trials 



VIII o seconds 100 



IX I " 145 



X 2 " 170 



XI 4 " 155 



XII 6 " 180 



Average 150 



lowing conclusions were reached : Judged on the basis of the 

 number of trials necessary to make the association, the difficulty 

 of the problem of transfer of response from light to sound 

 appears not to have increased proportionately with the increase 

 in time interval between the presentation of the two stimuli. 

 Practically the same increase in difficulty is manifest in going 

 from continuous presentation to the one-second interval as in go- 

 ing from the one to the two-second interval. The four-second 

 interval, on the other hand, seems easier to master than the two- 

 second but less easy than the one-second. The learning curves 

 start low, go through a short period of no learning, and then 

 rise rapidly in each group. 



B. Learning the Association in the Backward Direction. In 

 reading the literature on the phenomena of association one is 

 lead to the belief that psychologists generally hold to the con- 

 clusion that recall is predominantly in the forward direction. 

 Some experimental data, however, indicate that an association 

 will function backward as well as forward. Freeman found 

 that "the formation of an association between a stimulus and a 

 motor response by animals is exceedingly difficult and perhaps 

 impossible when the stimulus is presented after the act has oc- 

 curred." Since our method of procedure and experimental con- 

 ditions were so different it was decided to include an examination 

 of this point. 



Two groups of animals (Groups XIII and XIV) were used 

 in these experiments, the problem being the transfer of the pre- 



