Effects of d-amphetamine and cocaine on strained ratio behavior in a repeated-acquisition task.

The team gave rats d-amphetamine or cocaine while they learned a new chain of lever presses.

The rats had to finish 5, 20, or 50 presses to earn food.

Each day the order of presses changed, so the animals always had to learn a fresh pattern.

On the easy FR 5 schedule the drugs slowed the rats down and they made more errors.

On the tough FR 20 and FR 50 schedules the same drugs sped the rats up and their accuracy rose.

The harder ratio removed ratio strain, so the stimulants helped instead of hurt.

Harris et al. (1978) showed that d-amphetamine can either raise or lower response rate depending on the animal’s past reinforcement history.

Locurto et al. (1980) move that idea forward: the schedule itself, not just history, can flip the drug effect from bad to good.

Fisher et al. (2004) later found that cocaine tolerance looks the same across small FR pieces inside an FI schedule, backing the idea that ratio size controls drug impact.

McIntyre et al. (2002) also saw amphetamine cut high rates and lift low rates, matching the rate-dependency story seen here.

When you see sudden drops in accuracy or long pauses, check the ratio size before blaming the learner or the med.

A tougher response requirement may actually smooth performance under stimulant medication.

Try raising the ratio in small steps and watch if problem behavior and errors fall—you might turn strain into strength.