Effects of D-amphetamine in a temporal discrimination procedure: selective changes in timing or rate dependency?
Amphetamine smooths extreme response rates; it does not warp the internal timer.
01Research in Context
What this study did
Pigeons pecked a key for food. They had to learn when to peck.
The birds got tiny shots of d-amphetamine before some sessions. Doses ranged from 0.1 to 3.0 mg/kg.
Scientists watched if the drug changed the timing of pecks or just the speed.
What they found
High-rate pecking slowed down. Low-rate pecking sped up.
The pattern shows "rate dependency": the drug flattens extreme rates toward the middle.
The birds still knew when to peck. Their internal clock was not shifted.
How this fits with other research
Glover et al. (1976) saw the same flattening years earlier. Rats lost their timed pattern during a scary pre-shock cue. Both studies say baseline rate, not timing circuits, drives the drug effect.
Harris et al. (1978) went further. Rats with a history of fast responding slowed under amphetamine. Rats with a slow history sped up. McIntyre et al. (2002) echo this rule in a pure timing task.
McClure et al. (2000) looked like a clash. Methamphetamine hurt duration accuracy. But they used force changes and a different drug. Their task pulled response rate, so the result still fits the rate-dependency story.
Why it matters
If you run drug-behavior studies, check each animal’s baseline rate first. A "drug effect" may just be regression to the mean. Use steady schedules and watch for history effects before you blame the clock.
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02At a glance
03Original abstract
Two experiments evaluated rate dependency and a neuropharmacological model of timing as explanations of the effects of amphetamine on behavior under discriminative control by time. Four pigeons pecked keys during 60-trial sessions. On each trial, the houselight was lit for a particular duration (5 to 30 s), and then the key was lit for 30 s. In Experiment 1, the key could be lit either green or blue. If the key was lit green and the sample was 30 s, or if the key was lit blue and the sample was 5 s, pecks produced food on a variable-interval 20-s schedule. The rate of key pecking increased as a function of sample duration when the key was green and decreased as a function of sample duration when the key was blue. Acute d-amphetamine (0.1 to 3.0 mg/kg) decreased higher rates of key pecking and increased lower rates of key pecking as predicted by rate dependency, but did not shift the timing functions leftward (toward overestimation) as predicted by the neuropharmacological model. These results were replicated in Experiment 2, in which the key was lit only one color during sessions, indicating that the effects were not likely due to disruption of discriminative control by key color. These results are thus consistent with rate dependency but not with the predictions of the neuropharmacological model.
Journal of the experimental analysis of behavior, 2002 · doi:10.1901/jeab.2002.78-195