Unblocking in Pavlovian appetitive conditioning

Two experiments, with 280 Sprague-Dawley rats, demonstrated unblocking in an appetitive conditioning preparation. One stimulus, A, was first paired with either a low-value reinforcer (1 food pellet) or a high-value reinforcer (1 food pellet followed by 2 more food pellets). A 2nd stimulus, X, was then added to A, and the compound was reinforced with either the high- or low-value reinforcer. Conditioning to X was blocked if the same reinforcer was used in both phases of the experiment, but there was substantial conditioning to X when the reinforcer value was shifted either up or down when X was introduced. Exp I demonstrated this unblocking phenomenon using a design that minimized the potential contribution of generalization decrement. Exp II examined the effects of a variety of posttraining manipulations on conditioned responding to the added X cue after unblocking procedures. Among Ss that received downshifts in reinforcer value when X was introduced, responding was affected by several posttraining manipulations, including changes in context value. Those manipulations had smaller effects on the responding of Ss that received upshifts in reinforcer value and no effects on responding in control conditions. Findings are considered in relation to the model of conditioning outlined by R. A. Rescorla and A. R. Wagner (1972). (40 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).