I. 



INTRODUCTION 



The experiments reported in this monograph 1 are concerned 

 with three closely related problems in the field of animal psychol- 

 ogy : i) The influence of the time interval upon the rate of learn- 

 ing. The animals were divided into groups, and the terms X 

 and Y were presented in a temporal relation to each group. The 

 comparative number of trials necessary to establish a given 

 strength of functional connection constitutes the measure of the 

 relative efficacy of the several modes of presentation. 2) The 

 readiness with which a given temporal association will function 

 backward, and the most effective time interval for this function- 

 ing. The terms X and Y were here presented in the order Y-X, 

 but in the test experiments they were required to function in the 

 normal order X-Y. 3) The claims of the rival thories of simul- 

 taneous and successive presentation in relation to the rate of 

 learning. The animals were required to associate two factors, 

 X and Y. To one group the terms were presented simul- 

 taneously; to the others, successively. 



The nature of the present experiments may be further set 

 forth by additional explanation of the problems under considera- 

 tion. The various statements made in the modern texts on gen- 

 eral psychology indicate that simultaneous or successive presen- 

 tation is regarded as an essential condition for the formation of 

 an effective association. And by successive is meant immediate 

 succession; i.e., the two experiences must be in temporal contact 

 with each other. Our aim is to separate these terms by a certain 

 interval and observe its influence upon the rate of learning the 

 association when the terms are presented in the forward and 

 in the reverse order. Those who hold to the theory of simul- 



1 This research was begun in the Psychology Laboratory of The Uni- 

 versity of Texas in October, 1918, and continued until the following June, 

 at which time the work was transferred to the Psychology Laboratory of 

 The University of Chicago. 



