Central to research in Pavlovian conditioning over the last 30 years has been the issue of whether the temporal contiguity of events is or is not sufficient for associative learning. The current concensus is that it is not. This concensus is, however, now being challenged by a new and growing body of evidence. The new evidence suggests that contiguity may be sufficient for learning after all yet may be insufficient for the expression of that learning in performance. Three phenomena widely regarded as showing that contiguity is not sufficient for learning are blocking, overshadowing, and latent inhibition. Virtually all contemporary theories of learning view these phenomena as learning failures that occur despite favorable temporal contiguity. Using rat subjects, the proposed work would subject each phenomenon to three assays that have become standard tools for differentiating between learning and performance effects. The assays are blocking, second-order conditioning, and sensory preconditioning. The goal is to determine whether latent inhibition, blocking, and overshadowing really reflect learning deficits or whether they reflect performance deficits instead. Results supporting the performance-deficit-view would invalidate the mainstay assumption of nearly all modern theories of learning. Results supporting the learning- deficit view, would do so more strongly than any previous evidence. Results of either type would have direct relevance for Pavlovian conditioning models of human phobia. Such models have been criticized in part because the occurrence of trauma often fails to make people phobic about the situations in which the trauma occurred. Latent inhibition, blocking, and overshadowing are among the Pavlovian mechanisms that could explain these failures.
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