H. ENGER ROSVOLD AND MORTIMER MISHKIN 



559 



trial is never rewarded, and so on succeeding trials the animal must learn 

 to choose the other cue. Conversely, in the 'baited' condition the choice on 

 the fnst trial is always rewarded, and so on later trials the animal must 

 learn to choose the same cue. It has been demonstrated that in this situation 

 the monkey's initial response to each new pair of objects is frequently 

 determined by its preference for one object over the other. Thus, for the 

 animal, the difference between the two conditions is the difference be- 

 tween overcoming and persisting in an initial preference. Animals with 



TACTUAL DISCRIMINATION LEARNING 



500- 



250 



EFFORTLESS 



500 



tr 250- 



EFFORTFUL 



(ETTLINGER S WEGENER 1958) 



IROSVOLD, BATTIG, MISHKIN-UNPUBLISHED) 



Fig. 4 

 Effects of frontal lesions on tactual discrimination learning with two 

 different training procedures. 



frontal lesions do fnid it difficult to reverse their preference, as shown by 

 their poor performance in the 'unbailed' condition. They do not have 

 difficulty, however, in discriminating the objects, since their performance 

 in the other condition equals that of the normals. The evidence here is 

 clearly against ascribing to frontal animals a visual perceptual loss.^ 



It is possible to show that the same pattern of results can be obtained in a 

 tactual discrimination by manipulating another non-sensory variable. In 

 Fig. 4 it may be seen that when frontal monkeys are trained on tactual 

 discrimination with one procedure, they are impaired; with another 



^ It is perhaps worth indicating that such a loss can be assigned to animals with tcniporal 

 lesions, since they have been found to be equally impaired in both conditions. 



