8 K. S. LASHLEY AND L. E. WILEY 



(Thur stone, '30). In such situations the difficulty of the task 

 corresponds to its objective complexity and may be stated 

 quantitatively in terms of the number of items included in 

 the test series. 



In addition to this quantitative aspect of ' difficulty' there 

 are unquestionably qualitative elements. If the situation is 

 unfamiliar, if the stimuli are nearly indistinguishable, if the 

 integrations required are foreign to the native organization 

 of the animal, or if the relations to be recognized are obscure, 

 the difficulty of the task is increased. The maze studies 

 reported by Lashley ( '29) did not distinguish clearly between 

 number of similar elements and qualitative diversities. The 

 mazes differed in number of culs de sac, but also presented 

 fundamental differences in general plan, so that it is impos- 

 sible to determine which of the possible sources of difficulty 

 was predominant. 



In the present study we have attempted to devise a series 

 of mazes differing only in the number of similar elements 

 which must be learned and to test their relative difficulty 

 for normal and operated animals. 



Problems 



We may summarize the chief problems with which the 

 present study is concerned in the following questions : 



1. Is there a significant correlation between extent of cere- 

 bral lesion and degree of retardation in maze learning when 

 tested with an extensive series of cases? Confirmation of 

 this leads to the further problems : 



2. Is retardation a continuous function of the size of the 

 lesion, or is there a critical amount of injury below which 

 little effect can be observed? 



3. Are the effects of equal amounts of injury in different 

 cytoarchitectural fields the same for the learning of enclosed 

 mazes or are there characteristic differences in the degree of 

 retardation resulting from injury within different loci? 



4. With tasks differing in complexity (number of objectively 

 similar elements), what is the relation of the performance 



