Associative processes in differentially reared monkeys (Macaca mulatta): sensory preconditioning.

Past research has indicated that with regard to performance in formal learning test situations, early socially isolated rhesus monkeys display atypical reactions to noxious stimuli, deficits in response inhibition, slower adaptation to reinforcement contingencies, and lower performance on oddity tasks. Twelve adult rhesus monkeys (Macaca mulatta), 6 who had been reared in total isolation for the first 9 months of life 19 years earlier, and 6 socially reared, were tested in a sensory preconditioning paradigm. In phase I, two neutral stimuli (S1-S2) were paired in contiguous fashion; in phase II the S2 stimulus was conditioned to elicit a startle response; and in phase III the S1 stimulus was presented to assess whether an association between the two stimuli had been formed during the initial phase. Instead of a deficit, isolate subjects showed significantly more response transfer during phase III as compared to the controls. The superior performance displayed by isolates is viewed as resulting from a slower habituation to S1-S2 stimuli during preconditioning along with the perseveration of responses during testing. These findings support the notion that atypical cognitive processing across a lifespan is a consequence of early social impoverishment.