RONALD E. MYERS 487 



the trained eye. The three exceptional cases {Bsh, Brii, and Kiis) will be 

 discussed later (under Problem V) as examples of figural equivalence 

 effects affecting level of interocular transfer. 



From the above study it was concluded that there exists a well-ordered 

 system of intercommunication between the brain-halves exhibiting a 

 competence sufficient to handle experiential or gnostic information. 



PROBLEM II. WHAT IS THE NEURAL BASIS FOR THE VISUAL GNOSTIC INTER- 

 COMMUNICATION PROCESS? 



The corpus callosum seemed a most likely structure subserving such a 

 function because of its very large size and its relation as commissural 

 linkage par excellence between the cerebral hemispheres. Conversely, it 

 was difficult to delineate any other well-defined commissural system that 

 would likely be capable of such differentiated and complex contribution as 

 would seem necessary for the gnostic transfer activity. None the less, 

 review of the relatively few carefully controlled studies of corpus callosum 

 function yielded surprisingly few hints of defects following its total 

 destruction or absence in man or animal. 



Despite this disappointingly negative story derived from the literature, 

 interocular transfer tests were extended to cats having section of both the 

 optic chiasma and the corpus callosum. Cat Mniw, described above as 

 having demonstrated high level transfer of discrimination I-ab from the 

 right eye to the left eye, was one of six cats used in the present study and 

 may serve as an illustrative case. 



Following section of corpus callosum^ and a post-operative recovery 

 period of 21 days, Aliniii was taught discrimination Ill-ba while using the 

 right eye and Il-ab while using the left eye. He was then given 400 over- 

 training trials on each of these responses through the respective 'trained' 

 eyes. Final performance during overtraining was 40 correct in 40 with 

 discrimination Ill-ba and 38 correct in 40 with discrimination Il-ab. On 

 tests of transfer to the 'untrained' eyes performance on discrimination 

 Ill-ba was 20 correct in 40 trials and on discrimination Il-ab 19 correct in 

 40 trials. Performance was seen to drop from the consistent high level 

 obtained through the trained eye to a chance level through the untrained 

 eye. This remarkable result was similarly observed on tests run with the 

 other animals in this series in all instances but three (sec Table II). 



In one of these exceptional instances, performance was significantly 



' Along with section of the fibres of the corpus callosum there was always, in this study, 

 concomitant section of a contingent of fibres of the psalterium because of the hitter's close 

 apposition to the inferior surface of the corpus callosum in its posterior extent. 



