20 K. S. LASHLEY 



The slight differences in favor of the operated animals are 

 less than their probable errors and are not significant. 



In view of reported fluctuations in human behavior follow- 

 ing brain lesions, it seemed possible that the operations might 

 have produced a greater variability in the learning rates 

 of these animals, even though the means were unaffected. To 

 test this the standard coefficients of variation have been com- 

 puted for the normal and operated animals and are given 

 below. 



Trials Errors 



Normal animals, 0.479 ± 0.032 0.607 ± 0.041 



Operated animals, 0.380 ± 0.026 0.418 ±: 0.027 



Difference, 0.099 ± 0.041 0.189 ± 0.049 



The differences here are relatively larger than those between 

 the means. There is a suggestion that variability was actually 

 reduced by operation, but the differences are scarcely sig- 

 nificant. 



The lesions range in extent from 3.5 to 43.9 per cent of the 

 neopallium. In order to determine whether or not there is 

 a relation between the extent of injury and the rate of learn- 

 ing, the areas of the lesions have been correlated with the 

 learning scores for all cases. Spearman's formula for rank 

 order was used. The constants are given below. 



For lesions with trials, p = 0.132 ± 0.142 

 For lesions and errors, p = 0.088 ± 0.143 



The correlations are small and indicate that for the habit in 

 question there is no significant relationship between the extent 

 of brain injury and the ability to form the habit of reaction 

 to brightness within the limits of the experiment. 



From the data summarized in this section we may conclude 

 that lesions to the occipital areas of the rat's cerebrum, 

 whether slight or extensive, have no effect upon the ability 

 of the animals to form habits of brightness discrimination. 

 After complete destruction of the occipital third of the cortex, 

 visual learning progresses as rapidly as in normal animals. 



