RATE OF LEARNING IN THE WHITE RAT 35 



the same basis, it is more difficult to learn to associate a motor 

 response with an auditory stimulus when the latter is presented 

 one second after the former has occurred than when it is pre- 

 sented one second prior to the initiation of the motor response. 

 Under the latter condition Group III learned the association on an 

 average of 128.5 trials, while under the former conditions Group 

 XIV failed to make the association, although they had an average 

 of 340 trials. 3) When the stimuli are presented in immediate 

 succession it is more difficult for the association to function in 

 the backward than in the forward direction. To account for 

 the comparative ease with which the animals made the associa- 

 tion in the backward direction under these conditions, one may 

 assume that the new stimulus was not associated with the old 

 stimulus. This response and the new stimulus were experienced 

 simultaneously, and association is due to this simultaneity. 

 Summary : 



1. Association in the backward direction is only slightly more 

 difficult than in the forward direction when the terms to be asso- 

 ciated are presented in immediate succession. This small differ- 

 ence is by no means conclusive. 



2. It is much more difficult to learn an association in the 

 backward direction when the terms are separated by one second 

 than when they are presented in immediate succession. 



3. It is more difficult to associate a motor response with an 

 auditory stimulus when the latter is presented after the former 

 has occurred than when it is presented before- the initiation of 

 the motor response. 



4. The data found do not warrant the statement that it is 

 easier to associate a motor response with light than with sound 

 when the stimuli are presented in immediate succession. 



2. Simultaneous and Successive Presentation. The present 

 investigation was not undertaken primarily for the purpose of 

 gathering experimental data relating to the well known contro- 

 versy between simultaneous and successive association advo- 

 cates, but the condition of our problem made it profitable to 

 do so. Experimental data thus far reported are divided on this 



