498 BRAIN MECHANISMS AND LEARNING 



of correct response above and beyond that sustained by the more or less 

 incapable contralateral memory trace itself. 



No gross differences were seen among the cortical lesion types in their 

 effects on performance level through the opposite, 'untrained' neural 

 apparatus, as may be seen from Tables III and IV. Differences in perform- 

 ances were far greater within than between lesion types, and greater 

 deficits were not necessarily seen with greater lesions. This approximate 

 equivalence of the lesion types would support the concept that neural 

 tissue beyond the more restrictive removals contributes little towards the 

 maintenance, and possibly also the development, of stable contralateral 

 memory effects. 



It may be noted from Table V that corpus callosum section subsequent 

 to training did not affect performance on any discrimination on tests 

 through the initially trained eye. This was true whether the eye (and 

 hence the hemisphere) that underwent the tests was on the same side or 

 the side opposite to that utilized in the surgical approach to the corpus 

 callosum. From this it is apparent that the unilateral cerebral insult 

 incident tci the surgical approach to corpus callosimi did not compromise 

 the performance of either intrahemispheric mechanism for visual dis- 

 criminative response. Furthermore, this lack of effect of corpus callosum 

 section on the levels of learned performance through either hemisphere 

 speaks for a bilateral competence in visual learning and recall speaking 

 against the concept of unilateral cerebral dominance in visual learning 

 for the cat. 



PROBLEM IV. IS THE VISUAL GNOSTIC INTERCOMMUNICATION A GENERAL OR 

 LOCALIZED FUNCTION OF THE CORPUS CALLOSUM? 



The question of functional localization of the visual gnostic intercom- 

 munication process was investigated by extending transfer tests to cats 

 having varying extents of the anterior or posterior corpus callosum tran- 

 sected. The cats involved along with the nimiber of millimetres of corpus 

 callosum sectioned in each are given in Tables VI and VII. The percentage 

 figures given in parentheses represent the part of the total antero-posterior 

 extent of the corpus callosum included in each section. Each cat in the 

 series following post-operative recovery was monocularly taught and 

 standardly overtrained on discrimination Ill-ab. Final level of performance 

 in all cases was 38 or more correct in 40. In the last column of the tables 

 are given performances on the first consecutive days of transfer testing. 



As may be seen from Table VI section of up to 75 per cent (12.0 of 



