STUDIES OF CEREBRAL FUNCTION. IX 47 



that even the most extreme visual type, the eidetic, employs 

 visual mechanisms in routine learning to a greater extent 

 than do noneidetics. The assumption that differently local- 

 ized functions predominate in maze learning by different 

 animals, although possible, is not supported by any direct 

 evidence. 



The difficulty of the problem is increased by the clinical 

 evidence, especially in the field of aphasia. The conflicting 

 evidence on localization bespeaks a condition in man like that 

 which we find in our series of animals. Except for the pri- 

 mary projection areas, negative cases have been reported for 

 practically every cortical region. (Compare Monakow, '14, 

 p. 768, for a summary of the situation on motor aphasia and 

 Broca's area.) Negative cases in motor aphasia and similar 

 non-sensory functions cannot be explained plausibly in terms 

 of individual differences in the imagery used in speech. 



A significant point for the problem, perhaps, comes from 

 the repeated observation that the severity and duration of 

 symptoms from brain lesions are less in young than in old 

 and less in intelligent than in low-grade individuals. If true, 

 this can only mean that the severity of symptoms is dependent 

 not only upon the locus and extent of lesion, but also upon the 

 general level of dynamic functioning of the organism. 



In spite of the marked individual variation, the consistency 

 of the results on various functions presented in table 1 and 

 the uniform trend of the data summarized in figure 2 sug- 

 gest that there must be some constant causal factor in con- 

 sistency of maze performance dependent upon the mere 

 quantity of cerebral tissue and not an artifact arising from 

 the limitation of this or that special function. 



SUMMARY 



One hundred twenty-seven rats with cerebral lesions and 

 60 normal controls were trained in a maze of 8 culs de sac. 

 The learning scores in this task have been analyzed with the 



following results : 



