Drug effects on fixed-interval responding with pause requirements for food presentation.
Baseline response rate, not just reinforcement density, determines how drugs alter operant behavior.
01Research in Context
What this study did
The team gave rats two drugs on a fixed-interval schedule. They watched how fast the rats pressed a lever for food.
The twist: food only came if the rat paused first. This let them test how baseline speed changes drug impact.
What they found
Pentobarbital sped up slow presses and slowed fast ones. Amphetamine barely touched the slow presses.
The key point: the rat's own response rate, not just the schedule, shaped the drug effect.
How this fits with other research
Llewellyn et al. (1976) saw the same rate-dependency a year earlier on a very long 60-min FI. The pattern holds no matter interval length.
Sievert et al. (1988) swapped cocaine for amphetamine and still saw rate convergence, showing the rule applies across stimulants.
Dworkin et al. (1989) seem to clash: they found punishment history, not rate, guided pentobarbital's effect. Yet they matched baseline rates on purpose; M et al. let rates vary, so both studies highlight different levers—rate versus history—that drugs can pull.
Why it matters
If you track response rate before a medication change, you can predict who might speed up, slow down, or stay the same. Use brief probe sessions to map each learner's baseline, then watch for the flip predicted by rate-dependency. This simple check helps you decide whether a new behavior or a dosage tweak is driving session changes.
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02At a glance
03Original abstract
In pigeons performing under a multiple schedule of food presentation, low key-pecking rates (0.18 to 0.29 responses per second) were maintained during 3-min fixed-interval components by requiring a 4-, 5-, or 6-sec pause preceding the food-delivery response (tandem DRL), while higher rates (0.70 to 1.37 responses per second) were maintained in alternative fixed-interval components by requiring a pause of no more than 40 msec preceding the food-delivery response (tandem DRH). Thus, reinforcement density was equal but overall response rates markedly different in the two schedule components. Pentobarbital (3, 10 mg/kg) had effects on overall rates of responding consistent with a rate-dependency interpretation (low rates were increased while higher rates were decreased), but d-amphetamine (0.03 to 3 mg/kg) either failed to increase low overall rates in the tandem DRL components or increased them only slightly. Effects of both drugs on local responding within the fixed-intervals were always related in an orderly way to control response rate, but the extent of rate increases produced by d-amphetamine was modifed in some birds by pause requirements such that the drug increased comparable rates less when these occurred in the tandem DRL component than when they occurred in the tandem DRH components. Control rate is an important determinant of drug effects, independent DRH components. Control rate is an important determinant of drug effects, independent of reinforcement density maintaining rates, and independent of environmental influences, such as response-spacing requirements for food presentation, that can modify the extent of some drug-produced rate changes.
Journal of the experimental analysis of behavior, 1977 · doi:10.1901/jeab.1977.27-51