Effects of d-amphetamine, chlorpromazine, and chlordiazepoxide on intercurrent behavior during spaced-responding schedules.

Smith et al. (1975) gave rats three drugs while they worked on a spaced-responding schedule. The rats had to wait 20 seconds between lever presses to earn food. The team also watched what the animals did during the wait time, like drinking or running in a wheel.

They wanted to see if the drugs changed both the scheduled lever presses and the extra behaviors that filled the gaps.

The drugs changed lever pressing in a clear, orderly way across all rats. But the same drugs changed drinking and wheel running in ways that differed from rat to rat. Some animals drank more, some less, and some changed their wheel running in unique patterns.

In short, the main task responded predictably, while the side behaviors did not.

Hearst et al. (1970) tested the same two drugs in pigeons on the same schedule. They also saw mixed effects: low doses only slightly hurt timing, while high doses stopped responding. The 1975 rat study extends this work to a new species and adds collateral-behavior measures.

Billings et al. (1985) later showed that adding a clear stimulus can protect rat lever pressing from d-amphetamine disruption. Their finding helps explain why the main task in B et al. stayed orderly: the 20-second schedule itself gave strong stimulus control.

Lucki et al. (1983) confirmed that amphetamine increases or decreases behavior depending on the baseline rate, not on how often food arrives. This rate-dependency rule fits the idiosyncratic collateral changes seen in B et al.: each rat’s own baseline of drinking or running set the stage for its unique drug effect.

If you work with clients on medication, track more than the target skill. A drug may keep hand-raising accurate while side behaviors like stereotypy or water intake shift in unexpected ways. Collect simple counts of collateral responses to spot these hidden changes early.