Drug discrimination under a concurrent fixed-ratio fixed-ratio schedule.
Reinforcement ratio size can bend the dose-effect curve in drug-discrimination tasks.
01Research in Context
What this study did
Scientists trained pigeons to tell pentobarbital from salt water.
The birds pecked left after the drug and right after saline.
Two fixed-ratio schedules ran side-by-side; the size of the ratios changed across tests.
What they found
The pigeons stayed accurate, but the dose-effect curve bent with the ratio.
Tight ratios made the curve steep; loose ratios stretched it flat.
Schedule parameters, not just the drug, shaped the final numbers.
How this fits with other research
Bryant et al. (1984) first showed that ratio size can nudge pigeons toward the drug key even when no drug is present. The 1999 paper keeps the same bias idea and proves it can tilt the whole dose curve.
McMillan et al. (1997) used the same drug under concurrent fixed-interval schedules and still got clean discrimination. Together the two studies say, "The clock rules don’t matter; the ratio rules do for dose shape.
Louie (1980) saw pentobarbital flip a long-standing response bias. The new work flips the question: it asks how the bias flips the drug curve.
Why it matters
If you run drug-discrimination or any two-choice task, remember the schedule is a silent variable. A shift in ratio size can mimic or mask a dose change. Check your baseline bias before you credit the drug, and test at least two ratio values when you pilot.
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02At a glance
03Original abstract
Pigeons were trained to discriminate 5.0 mg/kg pentobarbital from saline under a two-key concurrent fixed-ratio 10 fixed-ratio 40 schedule of food presentation, in which the fixed-ratio component with the lower response requirement was programmed to reinforce responding on one key after drug administration (pentobarbital-biased key) and on the other key after saline administration (saline-biased key). After responding stabilized, pigeons averaged 98% of their responses on the pentobarbital-biased key during training sessions preceded by pentobarbital, and they averaged 90% of their responses on the saline-biased key during training sessions preceded by saline. In test sessions preceded by doses of pentobarbital, chlordiazepoxide, or ethanol, pigeons switched from responding on the saline-biased key at low doses to responding on the pentobarbital-biased key at higher doses (the dose-response curve was quantal). High doses of phencyclidine produced responding on both keys, whereas pigeons responded almost exclusively on the saline-biased key after all doses of methamphetamine. These and previous experiments using concurrent reinforcement schedules to study drug discrimination illustrate that the schedule of reinforcement is an important determinant of the shape of dose-effect curves in drug-discrimination experiments.
Journal of the experimental analysis of behavior, 1999 · doi:10.1901/jeab.1999.72-187