DRUG EFFECTS ON RESPONDING MAINTAINED BY STIMULUS‐REINFORCER AND RESPONSE‐REINFORCER CONTINGENCIES

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Abstract
The effects of pentobarbital and d‐amphetamine were assessed on key pecking by pigeons under conventional single‐key multiple schedules and under two‐key multiple schedules in which discriminative stimuli appeared on one key (stimulus key) while pecks on a second key (constant key) produced food. Pecks on the stimulus key had no scheduled consequences. A 60‐second variable‐interval schedule operated in one component of each multiple schedule; either extinction or a 60‐second variable‐time schedule operated in the alternate component. When the alternate‐component schedule was extinction, a high rate of responding was maintained in the variable‐interval component of the single‐key schedule; responding on both keys was maintained in the variable‐interval component of the two‐key schedule. Pentobarbital increased responding in the variable‐interval component of the single‐key schedule and increased stimulus‐key, but not constant‐key responding in that component of the two‐key schedule. When the alternate‐component schedule was changed to variable time, responding declined in the variable‐interval component of the single‐key schedule; stimulus‐key responding was no longer maintained under the two‐key schedule. Pentobarbital decreased responding in the variable‐interval component of both schedules. With an exception, d‐amphetamine only decreased responding in the variable‐interval component of the single‐ and two‐key schedules both when the alternate‐component schedule was extinction and when it was variable time. The results suggest that the effects of pentobarbital, but not d‐amphetamine, depend on the nature of the contingency (stimulus‐reinforcer, response‐reinforcer) that maintains responding.

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