Effects of promazine, chlorpromazine, d-amphetamine, and pentobarbital on treadle pressing by pigeons under a signalled shock-postponement schedule.

Scientists gave pigeons four different drugs. The birds had to press a treadle to delay electric shocks.

Each drug session used the same shock-postponement schedule. The team recorded how many times the birds pressed.

Promazine and chlorpromazine made the pigeons press more. Pentobarbital cut pressing almost to zero.

D-amphetamine produced small, mixed changes. Each bird reacted slightly differently to the same dose.

Bordi et al. (1990) later tested three of the same drugs in the same lab. They switched the task to key-pecking and added diazepam. Pentobarbital still lowered responding, but diazepam now increased it, showing that the response form matters.

Cohen (1991) gave d-amphetamine to pigeons working under a second-order schedule. The drug flattened response patterns but did not boost conditioned reinforcement, matching the small or null effects seen here.

Together, the papers show that drug effects on operant behavior are not fixed. The schedule, the response, and even the bird’s history can flip a result from increase to decrease.

If you ever consult on cases where medication meets behavior plans, remember this pigeon lesson. The same drug can raise or lower a target behavior depending on the task. Always baseline the response form before blaming or crediting the medicine.