Conditioning of the rabbit's nictitating membrane response to a CSA-CSB-US serial compound: manipulations of CSB's associative character.

Response acquisition to a trace conditioned stimulus (CSA) can be facilitated by insertion of a second stimulus (CSB) at the end of the trace interval just before the unconditioned stimulus (US). This effect may arise from serial mediation of trace conditioning, second-order conditioning, or both. Whereas serial mediation relies only on the presence of CSB, associative transfer relies on CSB's associative strength. In the present experiments, the presence of CSB was fixed, whereas CSB's associative strength was manipulated by (a) extinction of CSB, (b) latent inhibition of CSB, and (c) prior CSB-US pairings. In the first 2 cases, the level of responding to CSA was reduced in a fashion parallel to that of CSB. However, in the third case, partial blocking of conditioned response (CR) acquisition to CSA was observed. The results are discussed with reference to the role of associative transfer to both facilitating and blocking CR acquisition to CSA.