The CS− effect in simple conditioning and stimulus selection during development

Abstract

Changes in affect toward a particular stimulus can take place very rapidly through Pavlovian conditioning, if presentation of the conditioned stimulus (CS+) paired with the unconditioned stimulus (US) is accompanied by presentation of a “CS−,” another value of the same dimension as the CS+ but not paired with a US. This effect has considerable generality. It has been observed in terms of both olfactory and visual CSs, in terms of appetitive as well as aversive conditioning, and for adult as well as infant rats. The CS− effect has seemed especially important for infants, which may be related to the general tendency for infants to exhibit less stimulus selection than older animals. Finally, the CS− effect has enabled the development of a simple test of short-term retention that can quite effectively assess memory for either incidental or target events. These tests so far have indicated a clear ontogenetic decrease in rate of forgetting over short intervals, corresponding to the well-known development-related decrease in forgetting over long intervals (infantile amnesia). The tests also have shown that short-term forgetting of intentional and target events is surprisingly similar, with some indication of more rapid forgetting for the incidental events. Alternative interpretations of the CS− effect and some preliminary tests of these interpretations are discussed.