| There is an inherent confound when utilizing response-dependent chain schedules to examine conditioned reinforcement effects because the same response is required for the production of both conditioned and primary reinforcers. The present study utilized an observing response to examine the conditioned-reinforcing value of stimuli in a three-link chain variable-time schedule, which allows for the removal of the response-reinforcer contingency of typical chain schedules. In Experiment 1, observing was maintained by the production of stimuli correlated with links of a chain VT schedule, indicating conditioned reinforcing properties of all or some of the chain stimuli. To test if performance under chain schedules is maintained via backward transmission of reinforcer value (i.e., a classical-conditioning interpretation of chain performance), extinction and prefeeding conditions were implemented. No evidence of a backward transmission of reinforcer value was found when examining either the entire chain or just the first two links however, results were generally consistent with predictions based on the delay-reduction hypothesis. In Experiment 2, effects of d-amphetamine and morphine were tested to determine if the conditioned reinforcer efficacy of chain stimuli would be enhanced selectively by administration of a stimulant drug. Results did not support prior literature suggesting that only stimulant drugs enhance the efficacy of conditioned reinforcers, but were supportive of a rate-dependency interpretation. Overall, effects across drug and nondrug disruptors were consistent and suggest disruption of a common behavioral mechanism that may fit within the framework of a bipolar model of behavior within clocked interfood intervals. |
