Abstract: 1. Five normal rhesus monkeys were trained on object discrimination reversal, cylinder and cone were used as the discrimination throughout theexperiment. The rate of discrimination reversal learning, the immediatediscrimination after reversal (reversal phase) and the retention of discrimi-nation reversal (retention phase, 11 days) were observed. The results showedthat the rate of reversal learning and the percentage of correct reponses inreversal phase were improved in repeated training. Animals had also a goodperformance on discrimination task in retention phase. 2. Dorsolateral prefrontal cortex lesions impaired discrimination reversal.Bilateral lesions would result in impaired performance more severely thanunilateral ones. The prefrontal resected monkeys made more error trials inreversal phase and so decreased the rate of reversal learning retrainingtasks.

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