STUDIES OF CEREBRAL FUNCTION IN LEARNING. VII 



13 



(estimated 10 to 25 per cent) ; 3, severe (estimated 25 per 

 cent or more). Cases showing any lesion to the thalamus 

 were excluded from the series. 



EXPEEIMENTAL DATA 



Plan of experiments 



The problem involved the quantitative determination of the 

 effects of various lesions to the visual areas upon the rate of 

 formation of visual habits and upon the retention of visual 

 habits formed before the cerebral insult, with controls for 

 shock, diaschisis, and the like. The organization of the ex- 

 periment is summarized in table 1. Three groups of animals 



TABLE 1 

 Plan of experiments 



were trained, giving data upon separate points, but also 

 serving as controls for each other. These were : 



Group A. Male rats about 120 days of age were subjected 

 to lesion in the occipital region. Seven days after operation, 

 training was begun in the discrimination box and carried to 

 completion with ten trials per day. The training records of 

 the animals were compared with those of the following group 

 (trained before operation) to determine the average effects 

 of the lesions upon initial learning. The effects of lesions 

 of different size were also tested by correlation with training 

 records. 



Group B. Normal male rats about 120 days of age were 

 trained to perfect discrimination. They were then allowed 

 to rest for seven days, after which retention was tested (pre- 



