A MICROANALYSIS OF DRUG EFFECTS ON FIXED-RATIO PERFORMANCE IN PIGEONS

¹ Department of Radiation Biology and Biophysics, The University of Rochester School of Medicine and Dentistry, Rochester, New York

Pigeons trained to peck a lighted key on a fixed-ratio 30 (FR 30) schedule of food presentation received various dose levels of dl-amphetamine sulfate, sodium pentobarbital or imipramine hydrochloride. Performance was gauged in terms of the 30 interresponse times (IRTs) within the ratio. The first IRT of the ratio, the time between reinforcement and the first response, increased in a dose-related fashion after amphetamine and imipramine and decreased after pentobarbital. The subsequent IRTs displayed similar alterations after these drugs, but the magnitude of the effect depended, in part, on ordinal position within the ratio. Further analyses revealed that changes in the incidence of IRTs greater than one second ("outliers") correlated closely with the mean IRT changes, leading to the hypothesis that drugs mainly act on the cohesiveness of the FR pattern. Changes in the character of the interval histograms revealed further, more subtle alterations, which could be viewed as springing from changes in response topography.