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A conditioned suppression experiment was conducted with rats in an attempt to test the predictions offered by the Rescorla-Wagner (1972), Mackintosh (1975), and Pearce-Hall (1980) models regarding blocking effect. A four-stage within-subject design was employed in which rats received consistent pairings of a conditioned stimulus, CS A, with a weak shock in Stage 1. A simultaneous compound formed by the pre-trained CS A and an added stimulus CS B was paired with the weak shock in Stage 2. Subsequently, the same AB compound was paired with a stronger shock in Stage 3. A high level of suppression to CS A but no suppression to CSB was found in the final test phase. This pattern of results suggests that CS A blocked conditioning to stimulus CSB in both Stage 2 and Stage 3. This finding supports the predictions of the Mackintosh model, but not those offered by the Rescorla-Wagner and Pearce and Hall models
