d-amphetamine and fixed-interval performance: effects of operant history.
The same stimulant can either calm or excite behavior depending on the learner’s past reinforcement speed.
01Research in Context
What this study did
Scientists gave rats two different training histories. One group learned to press fast on a fixed-ratio schedule. The other group learned to press slowly on a spaced-response schedule.
Next, all rats worked on the same fixed-interval schedule. The team then gave each rat d-amphetamine and watched what happened to their lever pressing.
What they found
The drug did opposite things. Rats that used to press fast now pressed less. Rats that used to press slow now pressed more.
The rats’ past training set their everyday speed. That speed decided whether the drug would speed them up or slow them down.
How this fits with other research
LeFrancois et al. (1993) narrowed the claim. They showed that only the very last schedule, not old history, sets the rate that the drug then changes.
Glover et al. (1976) and Locurto et al. (1980) saw the same flip: high rates dropped, low rates rose, no matter if the task was fixed-interval or fixed-ratio.
McIntyre et al. (2002) swapped the drug for a short reinforcer signal and still got the same pattern, proving the key variable is local response rate, not the drug itself.
Why it matters
When you see a sudden change in a client’s behavior after medication, ask what their baseline rate was before the dose. A child who stims rapidly may slow down, while a child who barely responds may perk up. Check the pre-drug rate before you blame or credit the drug. This saves you from chasing side effects that are really just rate-dependency in action.
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02At a glance
03Original abstract
Sixteen rats were initially exposed for 50 sessions to either a fixed-ratio 40 or an interresponse-time-greater-than-11-second food reinforcement schedule, then shifted to a fixed-interval 15-second food reinforcement schedule. Animals with fixed-ratio 40 histories lever pressed at much higher rates under the fixed-interval schedule than did animals with inter-response-time-greater-than-11-second histories. This difference persisted across 93 sessions of fixed-interval exposure. The effects of d=amphetamine were assessed after 15 and 59 sessions of fixed-interval exposure. On both occasions, the low-rate responding of animals with interresponse-time-greater-than-11-second histories was typically increased by all doses of the drug, while the high-rate responding of animals with fixed-ratio 40 histories was typically decreased by all doses of the drug. These results suggest that control response rate under the fixed-interval schedule, which may be affected by a history of responding under another schedule, is the primary determinant of the relative effects of d-amphetamine.
Journal of the experimental analysis of behavior, 1978 · doi:10.1901/jeab.1978.29-385