H. ENGER ROSVOLD AND MORTIMER MISHKIN 



557 



modalities can hardly go unchallenged if the theory that the frontal lobes 

 are not concerned with sensory functions is to be maintained. 



Until recently, however, even these disturbnig results could be explained 

 away. Few of the early studies contained operated controls and so it was 

 possible to argue that a generalized impairment in all modalities simply 

 reflected a non-specihc post-operative disturbance which might be 

 expected to result from any large cerebral lesion. Contrast this with the 

 specific sensory-perceptual deficits which have been demonstrated after 

 selective ablations of the posterior 'association' cortex. For example, Pri- 

 bram and Barry (1956) and Wilson (1957) comparing directly the effects 



DISCRIMINATION LEARNING 



N-> 4 4 < 



(BRUSH a MISHKIN 1959 1 



N — » 3 2 2 



{WEISKRANT2 & MiSHKtN 1958) 



N— ► 3 •» 



[ETTLINGER 3 WEGENER .956) 



Fig. 2 

 Effects of frontal lesions on visual, auditory, and tactual discrimination learning 



oi intcrotemporal and posterior parietal lesions found a marked impair- 

 ment in visual discrimination following the temporal but not the parietal 

 lesion, and simultaneously, a marked impairment in tactual discrimination 

 following the parietal but not the temporal lesion. In comparison with 

 these specific deficits it seemed reasonable to argue, especially in view of 

 the absence of evidence to the contrary, that frontal lesions were produc- 

 ing only relatively minor, non-specific impairment, which was unrelated 

 to frontal-lobe function, per se. 



As shown in Fig. 2, however, the contrary evidence has now been 

 obtained. The discrimination impairment following frontal lesions may 

 be non-specitic as regards sensory modalities but it is specific to damage in 

 the frontal area and it is certainly not minor, hi fact, as these studies by 



