The interstimulus interval in classical autonomic conditioning of young infants.

Conditioned auditory discrimination and extinction of the skin potential response were attempted in 4-month-old infants using interstimulus intervals of 1500, 3500, 5500, and 7500 msec. Half of the infants in each of the interstimulus interval groups were defined as high magnitude orienters and half were low magnitude orienters. Conditioning was successful with the 5500- and 7500-msec interstimulus intervals, but not with the 1500- and 3500-msec intervals. Analysis of individual subject data indicated that individual subject data indicated that individual differences in conditionability were related to interstimulus interval and orienting response magnitude. Also, those subjects discriminating at the longer intervals tended to be high magnitude orienters. In other words, longer interstimulus intervals interacted with a high magnitude or orienting to facilitate conditioning. The results were taken as evidence that individual differences in the magnitude of the orienting response reflect different individual needs in stimulus information processing time.