1478 



II WDHtlOK OF l'HYSIl II i ICY 



Nl I Rl il'IIYSKJl.OCY III 



temporal sectors, there is usually some deficit in an 

 animal's ability to discriminate forms (2, 86, 203, 205, 

 242, 243). 



In recent years, there has been considerable interest 

 in the effect of ablations of the temporal (39, 40, 

 158-160, 188, 195, 204) and frontal (86, 167, 205, 

 24J, 243) lobes on the learning and retention of form 

 discriminations. Both lesions can produce impairments 

 with, on the whole, injuries to the temporal pole 

 being the more serious. On the other hand, depending 

 on the type of discrimination required of an animal 

 and on the size and locus of the lesion, there may In- 

 little or no impairment. Despite the great volume of 

 research of this type, the results do not yet form a 

 clear picture. 



[NTEROCULAR transfer. In contrast, a definitive and 

 interesting result is provided by some recent work 

 on the interocular transfer of visual discrimination 

 learning. Interocular transfer refers to the ability 

 to recognize with one eye what has been seen and 

 learned with the other. In this work, done with 

 cats (171, 172, 227), the animals were first subjected 

 to operations in which both the optic chiasma and 

 the corpus callosum were sectioned in the midsagittal 

 plane. This operation has the result of dissociating 

 each eye from its opposite visual cortex and the two 

 sides of the visual cortex from each other. After 

 operation, one eye of the animal was blindfolded and 

 training was carried out in the discrimination of 

 uch visual forms as a cross vs. a circle, horizontal 

 stripes vs. vertical stripes, etc. After the animal had 

 mastered the problem, the blindfold was transferred 

 to the other e\e. The result in ever) case was no 

 retention; the animal showed no memory at all of 

 what it had learned using the other eye. It was in 

 fact possible to train the animal to learn conflicting 

 habits with the two eyes with, s,i\ , .1 circle to the 

 li-ti eye positive and to the right eye negative. 



Normally , of < ourse, the mammalian retina projects 

 1., I mill v isual cortices. These experiments demonsti it 

 that, when this overlapping connection is eliminated, 



( alios. il association of the two cortices is essential 

 to remembering 'with one eve what has Keen learned 

 with the other.' This interesting result makes it clear 

 that the tnemorj ol .1 visual discrimination habit is, 

 undei these circumstances, confined to one side ol 

 the cert bral coi tex. 



\UDITOR> DISCRIMINATION. Studies ol .iiuhiorv dis- 



( rimination have mosl often employed a conditioned 

 avoidance technique (156, 186, igg . although there 



are some cases in which an animal has been required 

 to give a conditioned differential response to stimuli 

 (6, 239) or to locate the source of a sound in space 

 (185, 206). The last named technique yields measures 

 of auditory localization, whereas the former methods 

 are better suited to intensity and frequency discrimina- 

 tions. 



No matter what technique is employed, if an 

 animal is trained in a discrimination and then is 

 subjected to lesions of the auditory cortical areas, 

 it usually exhibits some loss of memory for the auditory 

 habit (59, 185, 186, 199, 206, 232). The amount of 

 loss varies with the size and placement of the lesion 

 and with the difficulty of the task. Unless the lesions 

 are too large, however, the animal usually can be 

 retrained to the preoperative level of performance 



(156). 



An animal with a large ablation of auditory and 

 associated cortex may, on the other hand, behave 

 differently in two auditory tasks (66, p. 518). Thus, 

 if two tones, A and B, are employed, cats will, after 

 such an operation, relearn to respond appropriately 

 to A as opposed to B (32). Relcarning of the dis- 

 crimination between the pattern of tones ABA and 

 BAB, however, is not possible (",1 I. This fact illustrates 

 an idea often expressed, namely, that the cortex is 

 required for discrimination learning when the task 

 is 'complex' but not when it is 'simple.' 



soMESTHETic DISCRIMINATION. The results obtained 

 for somesthetic discriminations .ire generally com- 

 parable to those summarized above for auditory 

 discriminations (208, 209, J39, 251 -253). In this case, 

 however, the relevant areas are somatic areas I and 

 II and, more generally, the posterior parietal lobule. 

 Sizable lesions anywhere in these areas usually cause 

 temporary impairment of habits acquired prior to 

 operation, but this typically can be effaced by some 

 refraining. It, however, the discrimination is made 

 relatively difficult, il the lesions Include .1 large por- 

 tion of both prim.irv and associative areas, or if both 

 of these conditions are present, the impairment 111. iv 

 be severe and m.iv not he ell, iced In ,mv amount of 

 training. 



One of the relatively lew studies on the effects ol 



cortical injur) in man on learning has been done 

 with somesthetic discrimination (76). Individuals suf- 

 fering unilateral penetrating injur) of the cerebral 

 hemispheres win 11. mud in making .1 tactual dis- 

 crimination ol different forms Normal individuals 

 using either hand and individuals with brain injur) 

 using the li. mil on the same side .is the lesion were 



