RONALD E. MYERS 497 



caJlosum section this cat (as well as Byr and Si!) was tested for contralateral 

 recognition of each discrimination using the untrained eye during which 

 high level performances were obtained. Corpus callosuni section was then 

 carried out and subsequent retention tests were run through both the 

 trained and untrained eyes. Again corpus callosum section caused no 

 essential change in performance level through the trained eyes. However, 

 on tests run through the untrained eyes a slight but definite low^ering of 

 performance was seen in the case of discrimination Ill-ba and a very large 

 and sustained lowering in performance in the case of discrimination Il-ab. 



Several important points emerged from these studies. The good contra- 

 lateral recall of the easier discrimination Ill-ab made it clear that the 

 'trained' hemisphere could induce lasting memory traces in the opposite 

 hemisphere, traces that subsequently may have an existence of their own 

 apart from transcallosal influences of the first hemisphere. Some lack of 

 definition or relative incapacity in this secondary trace mechanism was 

 hinted at, however, by the depression of initial recall of this easier response 

 occasionally seen through the untrained eye. The near failure of recall of 

 the more difficult discrimination Il-ab through the untrained eye insists 

 that when the differentiation handled is of greater subtlety the effects 

 across the midline through the corpus callosum are not sufficient to induce 

 a clearly defined secondary memory trace in the hemisphere not receiving 

 the sensory stimulation. The degree of success or failure obtained in 

 contralateral trace establishment seems, then, to depend in large part on 

 the difficulty of the discrimination handled. 



The impairment of recall through the untrained eye seen with lesions of 

 the 'trained' cortex or with post-training section of the corpus callosum 

 was not seen on similar tests run with these same discriminations in cats 

 with chiasma-section alone (compare results of Tables III and IV with 

 those of Table I, or compare pre- and post-operative transfer performances 

 of cats B(^ii>, Byr and Sll of Table V). The removal of critical cortex from 

 the initially trained hemisphere or the transection of corpus callosum 

 subsequent to training apparently removes an influence which normally 

 aids and abets performance through the untrained hemisphere at the time 

 of testing. Two contributions of the trained hemisphere to mnemonics 

 tested through the opposite untrained hemisphere must then be distin- 

 guished. One must occur prior to the disruption of the influence of the 

 trained hemisphere presumably at the time of initial training and results in 

 the induction of the secondary, somewhat less well-defined memory 

 mechanism. The second contribution appears to occur at the time of 

 actual testing of the contralateral mnemonics and results in the facilitation 



