Exposure to the unconditioned stimulus alone: effects on retention and acquisition of conditioned suppression

Three experiments demonstrated that repeated exposure to an electric-shock unconditioned stimulus (US) resulted in a decrement in retention of conditioned suppression evoked by a previously established excitatory conditioned stimulus (CS) and retarded subsequent acquisition of conditioned suppression to a novel CS paired with shock. Experiment 1 showed that 10 sessions of exposure to shock alone were required to produce a decrement in retention of conditioned suppression, whereas retardation in the acquisition of conditioned suppression was obtained following either 5 or 10 sessions of exposure to shock alone. Experiment 2 demonstrated that the magnitude of both the decrement in retention of conditioned suppression and the retardation in the acquisition of conditioned suppression produced by exposure to shock alone was directly related to the intensity of those shocks. Experiment 3 demonstrated that the decrement in retention of conditioned suppression produced by 10 sessions of exposure to shock alone was inversely related to the interval between the last exposure to shock and the test of the target CS. These findings are discussed in terms of associative and nonassociative accounts of the effects of US-alone procedures.