io JOSEPH U. Y ARE ROUGH 



the chief contributor. He reports a series of brief but suggestive 

 experiments. First, he reports three short experiments, all bear- 

 ing upon the subject of the influence of the time interval. White 

 rats were used in each of the experiments, and the same problem 

 box. The problem for the rats was to learn to choose between 

 two pathways to a food-box in a given temporal sequence, R, L, 

 R, L, etc. In case of incorrect choice the entrance to the food- 

 box was barred. Always the day's work began with pathway R. 

 Between the successive runs of a day's series the rats were 

 allowed to eat for a definite time interval. In the first experi- 

 ments three groups of eight rats each were used, and the inter- 

 vals for the groups were 15, 25, and 35 seconds, respectively. 

 The results indicate no essential differences between the groups 

 in the initial stages of the learning, and, indeed, no essential dif- 

 ferences throughout for the 15 and 35 second intervals. The 

 group tested on 25 seconds interval manifested a quite rapid rise 

 from the loooth to the i2OOth trial. This, however, is an in- 

 conclusive finding, as other factors than the time interval may 

 have influenced the result. The group was too depleted, unfor- 

 tunately, to permit of further continuation of the experiment. 

 In a second experiment three groups, six rats each, were tested 

 for intervals of 5, io, and 15 seconds, respectively. In this 

 test the entrances to the pathways R and L were alternately 

 blocked so that errors were impossible. Test series in which the 

 pathways were left open were interpolated every fifth day. 

 Thus the rats were forced to choose between the pathways and 

 the learning was measured by the number of correct choices 

 made in these test series. To quote the results : "The group dif- 

 ference is not very significant, but the results indicate that io 

 seconds is a more favorable interval than 15 seconds." In brief, 

 he admits that his findings are inconclusive as regards the in- 

 fluence of the time interval upon learning, but states that they do 

 prove that "an association nexus can be established over a con- 

 siderable interval of time," and that they make possible the ac- 

 ceptance of the hypothesis of direct connection between the 

 factors in successive association. 



