490 BRAIN MECHANISMS AND LEARNING 



direct afferent stimulation. This change has been called the memory trace. 

 Its stability is attested to by the uniformity of performance found day after 

 day during the periods of overtraining of the learned responses. Its 

 persistence is attested to by the fact of imaltered performance on testing 

 after periods free of training of up to a year. 



The effects of the monocular training on the 'untrained' hemisphere not 

 receiving the relevant direct afferent excitations are not known. Is a trace 

 system developed in this second hemisphere independent of that induced 



AAA 



Fig. 5 

 The normal cat can consistently discriminate the positive 

 central pattern (an equilateral triangle) from any of the 

 closely similar surrounding patterns (Sperry, Miner and 

 Myers, 1955). Compare this with the comparative coarseness 

 of the discriminations depicted in Fig. 4 some of which 

 begin to tax the discriminative capacity of the chiasma- 

 sectioned cat. 



in the first hemisphere receiving direct stimulation? If so, how do the two 

 trace systems compare in terms of definition or capacity r 



Explorations of these questions have been carried out in two ways : 

 (i) by transfer testing of chiasma-sectioned animals who have had ablation 

 of cortex from the 'trained' hemisphere subsequent to training, (2) by 

 transfer testing of chiasma-sectioned animals who have had complete 

 transection of corpus callosum subsequent to training. In this study two 

 underlying assumptions have been made: (i) the memory trace system 



