EFFECTS OF d‐AMPHETAMINE AND PENTOBARBITAL UNDER CONCURRENT FIXED‐RATIO SCHEDULES

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Abstract
Pigeons were studied under a 2-key concurrent fixed-ratio schedule of food presentation. During the first 5 sessions, the fixed-ratio requirements were 30 responses on 1 key (major key) and 120 responses on the other key (minor key): responding occurred almost exclusively on the major key. When the fixed-ratio requirements were then made equal at 30 responses on both keys, responding continued to predominate on the major key. The asymmetric distribution of responses persisted when the concurrent fixed-ratio fixed-ratio schedule was interrupted with periods during which the major key was associated with extinction while the other key remained associated with a fixed-ratio schedule. In some subjects the fixed-ratio requirements were increased. These schedule modifications decreased the asymmetry in responding but did not eliminate it. d-Amphetamine decreased rates on both keys and slightly increased the asymmetric distribution of responses, while pentobarbital reversed the distribution of responses by increasing low rates and decreasing high rates. The pigeons maintained their original asymmetric distribution and responses during the 1 1/2 yr/l study, despite schedule alterations and drug administrations.

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