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Perseverative errors in object discrimination learning by aged Japanese monkeys (Macaca fuscata).

To examine the nature of age-dependent cognitive decline, performance in terms of concurrent object discriminations was assessed in aged and nonaged Japanese monkeys (Macaca fuscata). Aged monkeys required more sessions and committed more errors than nonaged ones in the discriminations, even in simple object discriminations. Analyses of errors suggest that aged monkeys repeated the same errors and committed more errors when they chose a negative object at the 1st trial. A hypothesis analysis of behavior suggests that their incorrect choices were mainly due to object preference. Therefore, the impairment was probably caused by a failure to inhibit inappropriate responses. Together with previous neuropsychological findings, deficits of aged monkeys in the performance of object discriminations can be explained by dysfunction of the frontal cortex.

Age Factors↗

Value transmission in discrimination learning involving stimulus chains.

Rats learned a series of reversals of a positional discrimination in which responses to one lever led to delayed food and responses to a second lever led to no food. Interpolated within the delays leading to the different outcomes were two-link stimulus chains. The pairing of each stimulus element with the delayed outcome of food or no food varied across reversals. Either stimulus element could have the same correlation with outcome as occurred on the preceding reversal or the opposite correlation as on the preceding reversal. New reversals were acquired more quickly when both stimulus elements had the same status as during the preceding reversal, and were acquired most slowly when both stimulus elements had the opposite status as that of the preceding reversal. The rate of learning was intermediate when only one of the stimulus elements had the same status as that during the preceding reversal. All of the data are compatible with an interpretation in terms of backward chaining of stimulus value.

Animals↗