558 



BRAIN MECHANISMS AND LEARNING 



Brush and Mishkin (1959), Wciskrantz and Mishkin (1958) and Ettlingcr 

 and Wegener (1958) show, frontal lesions may, on occasion, produce 

 deficits in discrimination learning which are even greater than those 

 produced by lesions of the posterior area most closely associated with the 

 modality in question. It can no longer be argued that a frontal lesion 

 leaves discrimination learning unimpaired. 



What then becomes of the notion that frontal cortex is unrelated to 

 sensory discrimination functions ? The answer appears to be that it is still 

 correct, for a careful analysis reveals that it is, in fact, a non-sensory 



VISUAL DISCRIMINATION LEARNING 



UNBAITED 



BAITED 



100- 



IQO-, 



cc 50- 



N-» 4 4 N-^ 4 



(BRUSH a MISHKIN 1959) 



Fig. 3 

 Ertects of troiitdl lesions on visual discrimination learning 

 different training procedures. 



kith two 



deficit which underlies the frontal animals' discrimination impairment. 

 This conclusion is based on experiments showing that manipulation of 

 non-sensory variables determines whether or not the discrimination 

 learning of frontal animals will be impaired . 



In Fig. 3 for example, it may be seen that the identical animals, tested 

 on the same visual discriminations, are deticient when trained in one way 

 but not in the other. In both conditions there are a scries of discriminations 

 in which two objects are presented simultaneously for a few trials and the 

 monkey must learn which of the pair is rewarded. The difference between 

 the procedures is that in the 'un baited' ci>iidition tlie choice on the first 



