Backward sensory preconditioning.

Abstract

In Experiments 1 and 2, rats received initial training in which two neutral events were presented as a serial compound (A--~X). Subsequent training with A as a signal for shock was found to endow X with the ability to evoke the conditioned response of suppression. Experiment 2 also showed that responding to X was diminished if, prior to testing, Stimulus A underwent extinction. Two possible mechanisms for these findings are considered: (a) that X elicits responding through the associative chain X-A-shock, and (b) that A activates a representation of X that gains direct associative strength during conditioning with A and loses it during extinction of A. Experiment 3 demonstrated that an X-shock association established after initial A--~X training can be extinguished by nonreinforced presentations of A. These results suggest that associatively evoked representations of stimuli can enter into associations. In standard demonstrations of sensory preconditioning (e.g., Prewitt, 1967), subjects are given an initial phase of training with a serial compound event X-A, neither of the components of which has any marked motivational significance or response-eliciting power. In a second phase of training, one of the elements of the compound (A) undergoes standard Pavlovian training and, by virtue of its association with a motivationally significant unconditioned stimulus (US), comes to evoke an overt conditioned response (CR). In the final, test, phase of the procedure it is demonstrated that Stimulus X is also capable of evoking the CR. This result has been interpreted in terms of the formation of an association between X and A during the first phase of training. The second phase establishes an A-US association so that presentation of the X stimulus at test is able to contact the representation of the US (and thus evoke the CR) by way of the associative chain X-A-US. In addition, the effect can be found when A and X are presented as a simultaneous compound (e.g., Brogden, 1939; Rescorla & Freberg, 1978); in this case too, an excitatory X-A association could still be formed and might be responsible for the result observed. The remaining temporal arrangement (the backward case), in which A precedes the presentation of X, has been little studied; and to the extent that this procedure is less likely to generate the excitatory X-A association, it might be supposed that it would be unlikely to yield a sensory preconditioning effect. Indeed, with one exception, studies that have used backward pairings (i.e., A-X) in the first phase of training have failed to find any effect (Brown & King, 1969; Coppock, 1958; Tait, Marquis, Williams, Weinstein, & Suboski, 1969).