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



after cerebral lesion for a larger number of cases, as a basis 

 for a more reliable determination of the continuity and form 

 of the relation between extent of lesion and efficiency in 

 learning. 



The equivalence of different cortical areas for maze learning 



It seems quite clear from the results of Cameron ('28), 

 Lashley ( '29), Maier ( '32), and Jacobsen 2 that injuries in any 

 part of the cortex result in some retardation in the rate of 

 learning the maze. The relative effects of injuries in dif- 

 ferent cytoarchitectural areas remain uncertain. Lashley 

 ('29) attempted to measure the influence of injuries in dif- 

 ferent areas by comparing the numbers of errors made by 

 animals with lesions in different parts of the cortex, and 

 concluded that, within the limits of accuracy of the experi- 

 ment, the same amount of destruction within any area pro- 

 duced the same amount of retardation in learning. The 

 number of cases in his experiment was small, however, and 

 the average deviation of 13 per cent from equality between 

 the groups may have been really significant. Moreover, his 

 method of grouping cases resulted in a considerable overlap 

 of the areas compared and this may have tended to equalize 

 the averages of the arbitrary groupings. We have attempted 

 to deal more adequately with this problem of the relative 

 effects of lesions in different areas. 



The relative effects of lesions symmetrical and asymmetrical 

 in the two hemispheres 



All of the studies dealing with quantitative effects of cere- 

 bral lesions have dealt with lesions which were made as 

 nearly as possible symmetrical on the two hemispheres. Data 

 on the critical areas for pattern vision (Lashley, '31) and 

 unpublished data on maze retention after removal of one 

 hemisphere indicate that somewhat different results are to be 

 anticipated when the lesions are markedly asymmetrical. 



'Unpublished experiments on reversal of training. 



