110 K. S. LASHLEY 



persisted in climbing out of the discrimination box. On the second 

 day he responded promptly and found the food readily, but developed 

 a position habit which persisted for three more days. Training was con- 

 tinued until he relearned the problem. 



Postoperative retention tests, per cent error 65 



Number of trials required for relearning 74 



With errors distributed on successive days as follows 



3 (of 4), 6, 4, 9, 2, 0,3, 4, 0,0 



Lesion: Plate III, figure 11. On the right hemisphere the lesion 

 passed through the dorsal surface of the hippocampus and included 

 all the cortex laterad and caudad to this structure. On the left hemi- 

 sphere the lesion was less extensive and included only the cortex dorsad 

 and caudad to the hippocampus. 



Number 12. Small male, 115 days old. Trained in brightness 

 discrimination. 



Number of trials required for learning 60 



Preliminary retention tests, per cent error 0.5 



The occipital regions were destroyed as in other cases. Retention 

 was tested on the following day. He found the food readily and cor- 

 rected his errors promptly, averaging less than two seconds per trial. 

 During 60 trials on six successive days he gave no evidence of visual 

 discrimination. Retraining was not undertaken. 



Postoperative retention tests, per cent error 55 



Lesion: Plate III, figure 12. The dorsal convexity of both occipital 

 poles was destroyed. 



r* These three animals after extensive destruction in the occipital 

 region showed complete loss of the habit of visual discrimination. 

 Evidently the visual habit is mediated in some way by the occipi- 

 iL tal region and by the occipital region alone. Two of the three 

 / animals relearned the habit in normal time; the third was not 

 / tested adequately. The occipital lobes, though normally func- 

 tional, are not necessary for the formation of the visual habit. 



