Overshadowing the instrumental conditioning of a lever-press response by a more valid predictor of the reinforcer

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In Exp I, 16 male hooded Lister rats received an occasional brief response-contingent stimulus while leverpressing for food on a VI schedule. Presenting the stimulus concurrently with, and only with, reinforced responses produced a lower response rate than did presenting the stimulus equally often but uncorrelated with reinforcement. Exp II (24 Ss) revealed that the reinforcer-correlated stimulus reduced the rate of response in relation to that achieved by Ss receiving no stimulus presentations. Exp III (24 Ss) demonstrated the same effect with a stimulus from a different modality, and Exp IV, using Ss from Exp III, showed that this stimulus acquires the ability to maintain responding in extinction. Experiment V (32 Ss) demonstrated the suppressive effect of the reinforcer-correlated stimulus both when reinforcement for leverpressing was immediate and when it was delayed for 500 msec. Results are interpreted within a framework that assumes that instrumental learning involves the formation of a response-reinforcer association. The low rate of response produced by a stimulus correlated with reinforcement is attributed to the overshadowing of the response-reinforcer association by the formation of a stimulus-reinforcer association. (23 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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