|Abstract||The overexpectation effect (OXE) is the finding that following compound training with two asymptotic elements, X and A, animals respond less during tests of X or A alone compared to animals that did not receive such a compound treatment. During Pavlovian conditioning, the temporal relationship between a conditioned stimulus (CS) and an unconditioned stimulus (US) modulates both the nature (e.g., timing) and magnitude of the conditioned response (Catania, 1970; Roberts 1981). In three experiments, we used a conditioned magazine approach paradigm to evaluate the role of timing in the OXE. We hypothesized that the response decrement seen following overexpectation would manifest as temporally specific drops in magazine approach behavior during tests of X. In Phase 1, rats were given separate trials in which X (40 s in duration) and A (10 s in duration) signaled the arrival of a common US (e.g., sucrose). The delivery the US, moreover, occurred either 30s (Experiment 1), 15 s (Experiment 2) or 5 s (Experiment 3) after the onset of X. In Phase 2, we embedded A into X such that both elements signaled the same sucrose delivery, and consequently, the rats expected twice the sucrose. Tests of X revealed that rats responded less during the time periods in which sucrose was previously overexpected, as compared to rats that received only training trials of X alone in Phase 2 (Experiment 1 and 3) or trials with a novel element, C, embedded in X (Experiment 2). These are the first studies demonstrating a temporally specific OXE.