STUDIES OF CEREBRAL FUNCTION. IX 



of cases, and, although they do attest the importance of the 

 mass relationship, they give little further information con- 

 cerning it. Several purely statistical questions concerning 

 the relationship remain to be answered before we can make 

 -much progress in interpreting the functional significance of 

 the correlations. These questions call for a larger mass of 

 data than has been hitherto available and the primary aim 

 of the present study is to obtain a large series of cases, which 

 can be analyzed with some assurance of reliability. 



The continuity of the mass relationship 



The available evidence is not conclusive as to whether there 

 is a continuous progression in the effects of cerebral lesions 

 from the least to the greatest or whether there may be a 

 critical amount of destruction below which injuries are rela- 

 tively ineffective in producing deterioration. Several studies 

 (Lashley, '26, '29, table 11; Maier, '32 a and b) have given 

 indication of a sharp increase in the effectiveness of lesions 

 at about 15 to 20 per cent destruction. This may be evidence 

 for lower limit of extent of lesion necessary to produce signifi- 

 cant symptoms, but the appearance of a sharp rise in effective- 

 ness might also result, if the relation between extent of lesion 

 and deterioration had a logarithmic or other accelerated form. 

 Lashley ('26) found that the correlation ratio gave a higher 

 value (0.84) for the relation between lesion and amnesia than 

 did the correlation coefficient (0.72), indicating that the rela- 

 tionship is curvilinear, but with the small number of cases 

 the difference between these constants was not statistically 

 reliable. Thurstone ('33) has analyzed the data for maze 

 III of Lashley 's study ('29) and finds that the rate of learn- 

 ing is for this maze a function of the sixth power of the 

 intact cortex. Maier ( '32 a, b) has reported a very pro- 

 nounced drop in efficiency in reasoning tests with lesions 

 exceeding 18 to 20 per cent of the cortex. 



None of these studies provides sufficient material to deter- 

 mine the reliability of the form of the function. Our first 

 problem, therefore, has been to collect data on maze learning 



