Abstract

A new method was developed to study the effects of drugs on learning. In this each subject served as his own control. Pigeons worked for food reinforcenment in a chamber containing three response keys; all three keys were illuminated at the same time by one of four colors. For each session the pigeon's task was to learn a new four-response sequence by pecking the correct key in the presence of each color. After learning (within-session error reduction) had stabilized (40-60 sessions), this base line of repeated acquisition was used to assess the effects of drugs. The dose-effect data indicated that overall accuracy was impaired by phenobarbital, chlordiazepoxide and d-amphetamine arid that the degree of impairment generally increased as a function of dose. In contrast, chlorpromazine did not affect overall accuracy across the dose range tested, although there was a slight error-increasinig effect at the largest doses during the first part of the session. All four drugs increased pausing as a function of dose. Within-session analyses of the effects of the largest doses of phenobarbital, chlondiazepoxide and d-amphetamine indicated that the rate at which errors decreased was less in the drug sessions than in the control sessions.