Drug discrimination under concurrent variable-ratio variable-ratio schedules.
Under concurrent VR schedules, pigeons produce smooth, graded drug-discrimination curves that mirror probability matching.
01Research in Context
What this study did
Carr et al. (2002) trained pigeons to tell pentobarbital from saline.
Birds pecked on two side keys under concurrent VR VR schedules.
Each key paid off after a different average number of pecks.
What they found
Dose-response curves were smooth slopes, not all-or-none jumps.
The birds acted like they matched their pecking to the payoff odds.
Graded curves looked more like interval schedules than fixed-ratio ones.
How this fits with other research
Dougherty et al. (1996) saw the same smooth curves with a simple concurrent schedule.
Lancioni et al. (2000) later switched to rats and VI schedules; unequal ratios kept control.
Together the three studies show: smooth drug curves appear across species, schedules, and reinforcer ratios.
Why it matters
If you run concurrent schedules in the lab, expect graded choice data, not sharp switches.
Use unequal reinforcer ratios to keep stimulus control tight.
The payoff odds, not the drug dose alone, shape the bird’s (or client’s) allocation.
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02At a glance
03Original abstract
Pigeons were trained to discriminate 5 mg/kg pentobarbital from saline under concurrent variable-ratio (VR) VR schedules, in which responses on the pentobarbital-biased lever were reinforced under the VR schedule with the smaller response requirements when pentobarbital was given before the session, and responses on the saline-biased key were reinforced under the VR schedule with the larger response requirements. When saline was administered before the session, the reinforcement contingencies associated with the two response keys were reversed. When responding stabilized under concurrent VR 20 VR 30, concurrent VR 10 VR 40, or concurrent VR 5 VR 50 schedules, pigeons responded almost exclusively on the key on which fewer responses were required to produce the reinforcer. When other doses of pentobarbital and other drugs were substituted for the training dose, low doses of all drugs produced responding on the saline-biased key. Higher doses of pentobarbital and chlordiazepoxide produced responding only on the pentobarbital-biased key, whereas higher doses of ethanol and phencyclidine produced responding only on this key less often. d-Amphetamine produced responding primarily on the saline-biased key. When drugs generalized to pentobarbital, the shape of the generalization curve under concurrent VR VR schedules was more often graded than quantal in shape. Thus, drug discrimination can be established under concurrent VR VR schedules, but the shapes of drug-discrimination dose-response curves under concurrent VR VR schedules more closely resemble those seen under interval schedules than those seen under fixed-ratio schedules. Graded dose-response curves under concurrent VR VR schedules may relate to probability matching and difficulty in discriminating differences in reinforcement frequency.
Journal of the experimental analysis of behavior, 2002 · doi:10.1901/jeab.2002.77-91