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



reliably measure some function which is common to the learn- 

 ing of different mazes. 



ANALYSIS OF EXPEEIMENTAL DATA 



Deterioration after cerebral lesion 



The training records of all operated cases are summarized 

 in tables 4, 5, 6, and 7 and the details of the lesions are shown 

 in plates 1 to 5. The numbers and arrangement of the figures 

 in the plates correspond to the experimental numbers of the 

 animals in the tables, for ready reference. Similar data for 

 normal animals trained under parallel conditions are given 

 in tables 8, 9, 10, and 11. 



The mean scores for the various criteria, with probable 

 errors of the means and standard deviations of the distribu- 

 tions, are summarized in table 12. With average destructions 

 of 20 to 25 per cent, the operated animals require from 2 to 

 17 times as much practice to reach the criterion of learning 

 as do normals. The greatest differences are in the numbers 

 of errors, the least in the numbers of trials. Since training 

 was discontinued after 150 trials, the average of trials for 

 the operated cases does not express the actual retardation. 

 Fifty-one of the operated animals failed to reach the criterion 

 in mazes I to IV, and 47 in maze V, and the scores for trials 

 would have been very much higher, if these animals had been 

 trained to errorless running. The error scores, therefore, 

 probably represent most truly the difference between the 

 normal and operated groups. Judged by this criterion, the 

 latter require from 7 to 17 times as much practice as the 

 former. 



A comparison of table 12 with table 15 reveals that there 

 is retardation, even for the smallest amounts of injury. 

 Animals with lesions of less than 10 per cent of the neocortex 

 required 153 per cent as much practice, measured in terms 

 of errors, as did normals. 



All these differences between normal and operated groups 

 are statistically reliable. They demonstrate that cerebral 

 lesions produce a significant reduction in the capacity for 

 maze performance, even when the lesions are quite small. 



