Deficits In Visual Discrimination Research Articles

Further analysis of visual discrimination deficits following foveal prestriate and inferotemporal lesions in rhesus monkeys.

Further analysis of visual discrimination deficits following foveal prestriate and inferotemporal lesions in rhesus monkeys.

Effects of endbrain lesions on visual discrimination learning in pigeons.

While there has been considerable study of the avain forebrain, we still have little understanding of its role in behavior. Zeigler (1963) found that lesions restricted to hyperstriatal areas produced deficits in pattern and intensity discrimination. Because this region is itself composed of two areas, a hyperstriatum and an accessory hyperstrian~m, it was not possible to determine to which area the deficits were attributable. The present study was designed to investigate the role of these two areas in visual discrimination learning by training 12 adult male pigeons to 90% criterion for 50 trials on two consecutive days to make pattern (triangle vs circle), intensity (high vs low), and color (red vs green) discriminations in key pecking, balancing stimulus and transfer effects. Ss were then divided into four surgical groups (unilateral and bilateral lesions for each area) and retested. Ablation of either accessory hyperstriatum produced deficits in visual discrimination confirming the findings of Zeigler (1963). While unilateral lesions were not accompanied by deficits, bilateral lesions of accessory hyperstriatum produced deficits in pattern discrimination (p < .08) and bilateral lesions of hyperstriatum produced deficits in color discrimination (p < .08). These results suggest that the deficit^ produced were more a function of the extent of the lesion rather than its loczls. Ss with lesions in accessory hyperstriatum showed no differences in color or intensity discrimination, and Ss with lesions in hyperstriatum showed no differences in pattern or intensity discrimination. Examination of the learning curves for these Ss indicated that the original learning on those tasks in which no deficit was produced was better, suggesting that the magnitz~de of the deficit was, in paTt, a function of difficulty in original learning and inherent problem difficulty rather than the specific cype of problem, i.e., pattern discrimination. It was also noted that positive and negative transfer effects in the sequential presentation of problems with similar elements conuibute to retention after ablation as well as original learning. It, therefore, seems methodologically important to minimize transfer effects when studying the effects of ablation on learning.

TEMPORAL LOBE LESIONS AND MEMORY IN THE MONKEY.

IN 1954 Mishkin and Pribram1,2 demonstrated that removal of the inferotemporal cortex in the monkey produced a severe visual discrimination deficit. Subsequent studies have investigated the parameters of this deficit, but its basic nature is still not clear3–7. Since 1954 considerable clinical evidence has accumulated showing that bilateral ventral medial temporal lesions are associated with a severe memory loss in man, characterized by a difficulty in retaining new information for more than a brief period8,9. It has been suggested that bilateral removal or injury to the hippocampus and the nearby ventral neocortex is responsible for this deficit. In view of the fact that during the evolution of the primate temporal lobe there has been an enlargement of the neocortex and subsequent lateral-ventral movement of tissue10, it is our hypothesis that inferotemporal lesions in the monkey may in some degree be analogous to the more medial lesions in man and that inferotemporal monkeys fail discrimination learning tasks because of inability to store visual information.