T. PINTO HAMUY 



595 



cortex was within the range of the critical amount necessary to provoke 

 the faikire to learn. 



The 'posterior group' with a lower average of ablated cortex presents, 

 however, a clearer deficit than the 'anterior group'. Both groups differ 

 significantly from one another in their performance (p < 0.05). These 

 results would indicate that the locus of lesion can also be regarded as a 

 relevant factor. In other words, the involvement of the visual area would 

 determine a greater incapacity than similar lesions in other areas. It 

 should be noted, however, that none of these animals had the visual area 

 totally ablated. The amount of visual cortex removed in the various rats 



5 10 15 20 25 



ten trial units 



Fig. 6 

 Learning curves of a VCR corresponding to the following 

 groups of rats: normal, 'anterior', 'posterior' and decorticated. 



ranged from a minimum of 60 per cent to a maximum of 92 per cent. 

 On the other hand, the performance of the group combining both lesions 

 was inferior to that of the group with the posterior lesion. It is probable, 

 therefore, that the whole of the cerebral cortex — both the specific as well 

 as the rest of it — plays a role in this type of learning. Summing up, both 

 factors, namely the extent of lesion and its locus, seem to have an influence 

 in this respect. 



The fact that some animals of the 'posterior group' with a removal of 

 only 23 or 31 per cent of the total cortex and 70 and 78 per cent respec- 

 tively of the visual cortex were unable to learn this lACR would suggest 

 that this failure is not exclusively due to the locus or extent of the lesion 

 but to some characteristic of the experimental situation that requires a 



QQ 



