Effects of conditioned stimulus presentation on diminution of the unconditioned response in aversive classical conditioning

The purpose of this experiment was to study whether conditioned diminution of the unconditioned response (UR) is a phenomenon with an associative basi s. Discriminative electrodermal conditioning was used with an interval betw een the conditioned stimulus (CS) and unconditioned stimulus (US; aversive white-noise) of 8 s. Fifty-nine volunteer subjects received discrimination training in which one CS was reinforced (CS + /US) and a second CS was non- reinforced (CS -). After this discriminative training phase, participants w ere tested using intermixed trials in which a US was preceded by either a C S +, a CS -, or a neutral stimulus (NS). The results indicated that the ski n conductance response amplitude of the UR was lower when the US was preced ed by the CS + than when the US was preceded by the CS - or the NS. However , NS/US presentations elicited URs of greater amplitude than those of the C S - /US presentations. The results can be explained in terms of orienting r eflex reinstatement. In addition, it is argued that conditioned diminution has an associative basis. (C) 1999 Elsevier Science B.V. All rights reserve d.