CEBEBKAL FUNCTION IN LEARNING 109 



This animal showed perfect retention after operation. Open- 

 ing the skull in the occipital region does not produce sufficient 

 shock to cause loss of the habit. 



Group 4- Occipital region destroyed. 



Number 10. Small male, 114 days old. Trained in brightness 

 discrimination. 



Number of trials required for learning 60 



Preliminary retention tests, per cent error 2.5 



The occipital lobes were injured by passing a knife backward from 

 openings in the skull, like those in number 9, to the base of the skull, 

 avoiding injury to the thalamus and cerebellum. Retention was 

 tested on the following day. The animal was active and gave little 

 evidence of discomfort. He went through the problem box promptly 

 and without hesitation. He found the food readily and corrected his 

 errors promptly, but he made six errors in ten trials. On the following 

 day his behavior was like that of an animal in the early stages of train- 

 ing. He retained all of the habits of the discrimination box except 

 that of visual discrimination. Retraining was begun and for four days 

 he gave no evidence of discrimination. He then improved until the 

 reaction was reestablished. 



Postoperative retention tests, per cent error 50 



Trials required for relearning 100 



With errors distributed on successive days as follows 



6, 5, 5, 3, 3, 0, 1, 0, 2, 2, 0, 



Lesion: Plate III, figure 10. On the left the lesion included all of 

 the cortex caudad to the plane of the posterior limit of the hippocampus. 

 On the right the mesial surface of the occipital lobe remained intact. 



Number 11. Small male, 107 days old. Trained in brightness 

 discrimination. x 



Number of trials required for learning 60 



Preliminary retention tests, per cent error 2.5 



The occipital lobes were injured by an operation similar to that on 

 number 10. Retention was tested on the day following operation. 

 The animal was very active, extremely hungry, and when he reached 

 the food ate voraciously. He seemed unable to adjust himself to 

 making the turn into the food compartment and after the fourth trial 



