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This report summarizes a program of experiments on the behavior of braindamaged monkeys. The ablations of the animals comprise extensive destruction of one hemisphere combined with decortication of either the contralateral prefrontal or parieto-temporo-preoccipital regions.All the tasks investigated were varieties of delayed-response and discrimination problems. The studies were designed to further the analysis of the differential effects of anterior and posterior lesions upon performance in the two situations and to discover procedures that might enable monkeys with prefrontal lesions to perform efficiently on delayed-response tests.It has already been shown that the monkeys with the additional frontal destruction have difficulty with delayed-response problems (10), whereas the animals with the additional posterior ablation are less efficient than normal controls in the solution of discrimination problems (13). Furthermore, the monkeys of the first group have very little trouble with discrimination problems (10), in keeping with earlier findings (4). To complete a picture of differential frontal and posterior syndromes, it is necessary to demonstrate that monkeys with posterior lesions are capable of delayed response. Jacobsen (4) believed that posterior lesions did not affect delayed response, but his position was questioned by Lashley (5), who found that some monkeys with ablations of the prestriate cortex could not perform delayed reactions. Lashley concluded that the delayed-response problem provides no basis for distinction between the functions of the anterior and posterior association areas. His conclusion has not, however, been confirmed by Meyer, Harlow, and Ades (9) or by Blum, Chow, and Pribram (1) except for the finding by the latter investigators that one monkey with isolated bilateral destruction of the tip of the temporal lobe could not be trained to solve delayed-response problems. Thus, the question is far from settled.Experiments are described which demonstrate that massive posterior ablations which produce a lasting decrement in discrimination learning do not necessarily impair delayed response. It should be noted that this datum is useful from the standpoint of control for sensory loss, because demonstration of the adequacy of the visual system for the delayed-response situation is a very effective way to combat the interpretive difficulties that are born of the interruption or probable interruption of parts of the optic radiation.The second phase of the investigation concerns the effects of variations in the

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