366 K. S. LASHLEY 



experimental investigation. The existing studies demonstrate 

 the superior efficiency of distributed practice but give no clue to 

 the reason for it. 



The inferences drawn from studies of the rat in the maze can 

 not be extended to embrace learning of other types without 

 further study. But the studies with the maze are the only ones 

 in which definite evidence as to the mode of action of the dis- 

 tribution of practice has been obtained. The experiments re- 

 ported here and in the previous study seem to demonstrate that 

 the greater part, if not all, of the effect of concentrated practice 

 in maze-learning is due to the development of habits which inter- 

 fere with efficient performance, either by limiting trial movements 

 or by causing actual avoidance of the correct path. In both 

 cases the interference is with the process of adjustment and not 

 with that of fixation. 



In other forms of learning there are many agents which such as 

 fatigue and loss of interest in long practice periods which may 

 interfere with efficient performance and so prolong the apparent 

 learning tune, while with verbal habits the possibility of practice 

 outside of the experimental practice periods has not been alto- 

 gether eliminated where short practice periods were used. There 

 is thus a possibility that in all forms of learning the results of 

 distribution of practice are due, not to any fundamental principle 

 in the fixation of nervous integrations, but to wholly incidental 

 factors arising from the particular conditions of training in each 

 case studied. The evidence obtained with the maze lends some 

 probability to this view; sufficient, at least, to preclude the use 

 of such a blanket explanation as the gradual ' set ting' of new ner- 

 vous connection before the influence of other factors has been 

 investigated. 



SUMMARY 



1. The simple maze, including a single cul de sac, provides as 

 reliable an index to the rate of fixation of habit in differentially 

 treated groups of animals as does the more complicated circular 

 maze. 



