Chronic fear produced by unpredictable electric shock

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16 Sprague-Dawley male albino rats, having learned to bar press for food, received CSs paired with electric shocks. For 1 group CSs and shocks were randomly interspersed, then new CSs predicted shocks; these Ss stopped bar pressing completely and formed extensive stomach ulcers. The group for which all shocks were predicted by CSs showed only transitory disruption of bar pressing and formed no ulcers. Experience with randomly interspersed CS and shock retarded acquisition of a conditioned emotional response when a new CS predicted shock. Implications for the following are discussed: (1) a safety-signal explanation of the disruptive effects of unpredictable shock, (2) the learned helplessness hypothesis, and (3) the appropriateness of the random control group in conditioning. (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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