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Effect of Previous Exposure on Response Decrement Induced by an Olfactory Stimulus

Two experiments examined the influence of pre-exposure on the decrement produced in a trained running response by a novel odor. In Exp. 1, when first presented in the runway, the smell led to higher running times in a group of rats pre-exposed 72 hr. earlier and in a group with no pre-exposure than in a group pre-exposed 25 min. earlier. There was no significant difference between the first two groups. In Exp. 2, three groups of rats were pre-exposed, 25 min. before testing in the runway, in pre-exposure boxes which differed in degree of similarity to the runway. Their performance did not differ significantly on test sessions. Taken together, the results indicate that contact with a novel odor is sufficient to lessen its decremental effect even if it occurs outside the training situation and is not followed by reinforcement. The effects of pre-exposure dissipate with time and do not seem to depend strongly on contextual stimuli.