Effects of body weight on discriminative-stimulus control by phencyclidine in the pigeon.

Researchers tested whether hunger level changes how pigeons react to the drug phencyclidine. They kept birds at three body weights: 70%, 80%, and 90% of their free-feeding weight.

While at each weight, pigeons learned to peck one key when given phencyclidine and another key when given saline. The team then checked if the birds still chose the correct key when given different doses.

The pigeons stayed accurate no matter how hungry they were. Their drug-versus-saline choices and generalization curves looked the same at every weight level.

Hunger cues did not compete with the drug cue. The phencyclidine stimulus stayed in full control of the birds' key pecks.

Sailor (1971) showed the opposite: when pigeons were hungrier, their peck rates changed more between reinforcement and extinction. The difference is the task. W trained birds to tell red from green lights; hunger shifted response rates but not color choices. Timberlake et al. (1987) trained birds to tell drug from no-drug; hunger shifted neither rates nor choices.

Sobsey et al. (1983) also used drug cues in pigeons and got tight stimulus control, matching the 1987 result. Together the studies say drug stimuli are robust; they hold their power across hunger, dose history, and even different drugs.

Madden et al. (2003) later showed the same stability in rats: cocaine self-administration stayed under tight stimulus control using schedules like those in the pigeon work. The pattern spans species and drugs.

If you use drug-discrimination or any chemical cue in a single-case design, you can be confident that mild food restriction will not muddy the stimulus control. You do not need to keep motivation perfectly constant across sessions. This frees you to adjust reinforcer amount or session length for other experimental goals without fear of weakening the stimulus.