Behavioral and pharmacological influences on phencyclidine discrimination in the pigeon

Discriminative stimuli produced by drugs control behavior in the same way as exteroceptive discriminative stimuli control behavior, despite the difficulty in controlling the intensity of the discriminative stimulus properties of drugs throughout test sessions. In recent years, many investigators have correlated the potency of drugs as discriminative stimuli, with their affinity for specific pharmacological receptors. High correlations have been interpreted as evidence that the discriminative stimulus properties of drugs are mediated by these specific pharmacological receptors. However, the relationship between discriminative stimulus potency and receptor affinity can be confounded by other pharmacological effects of drugs, such as their ability to produce position responding, and by behavioral variables, such as the schedule of reinforcement under which the drug discrimination is established and measured.