CEREBRAL FUNCTION IN LEARNING 83 



difference in pattern remained. No one of the animals con- 

 tinued to discriminate on the basis of pattern or could be 

 trained to the discrimination within 600 trials. 



The absolutely identical learning records in the Yerkes 

 box for animals with and without the visual cortex seems to 

 constitute clear evidence against the hypothesis. The aver- 

 age for eighty-nine normal animals in this problem is 131 

 trials, 44 errors, and for 113 animals lacking parts or all of 

 the visual cortex is 123 trials, 41 errors. It is almost incon- 

 ceivable that the animals of these two groups were forming 

 the habit upon the basis of different aspects of the stimuli, 

 since under conditions where habits based upon both bright- 

 ness and pattern have been demonstrated, there is a signifi- 

 cant difference in the rate of formation of the two in normal 

 animals, and animals lacking the visual cortex fail to form 

 the habits of pattern discrimination with any amount of 

 practice. 



These considerations seem to eliminate the persistence of 

 varying degrees of peripheral vision as an explanation of 

 the quantitative relations found and to necessitate the as- 

 sumption of some dynamic influence of the striate areas in 

 the function of brightness vision, which is independent of 

 the detailed spatial differentiation of the areas exhibited in 

 pattern vision. 



SUMMAEY 



The discovery that pattern vision is conditioned by a small 

 lateral area for the visual cortex of the rat has made it pos- 

 sible to test whether or not the relationship between extent 

 of cerebral destruction and the degree of postoperative 

 amnesia for the habit of 'light-darkness' discrimination, re- 

 ported earlier, was due to the invasion of this critical area by 

 larger lesions. The data previously reported have been 

 analyzed in relation to this critical area with the following 

 results : 



1. Lesions which do not involve the area essential to pat- 

 tern vision probably do not produce any postoperative am- 

 nesia for the brightness habit. 



