THE EFFECTS OF SMOKED MARIJUANA ON PROGRESSIVE-INTERVAL SCHEDULE PERFORMANCE IN HUMANS

In three experiments, 8 human subjects participated in a study of the effects of smoked marijuana on progressive-interval schedule performan ce. A two-component chained progressive-interval fixed-interval schedu le of point delivery was used. In the progressive-interval component, the interval length began at 20 s and increased either geometrically o r arithmetically (by either 20 s, 40 s, 80 s, 100 s, or 160 s) on each subsequent interval. After this interval elapsed, a single button pre ss produced the fixed-interval component, with a total of five reinfor cers of varying magnitude ($0.05, $0.20, or $0.40) available on a fixe d-interval 20-s schedule. After the five reinforcer deliveries, the sc hedule returned to the initial progressive-interval component. Several relationships were found among rates of responding, postreinforcement pauses, and drug administration in the progressive-interval component : (a) Postreinforcement pauses increased as the temporal requirements of the progressive-interval schedule increased; (b) rates of respondin g during successive progressive-interval components rapidly decreased to low rates of responding after the first few progressions; (c) postr einforcement pauses decreased systematically as dose of smoked marijua na increased; and (d) rates of responding increased after smoking acti ve marijuana but not after smoking placebo cigarettes. Results are dis cussed in the context of behavioral control and relevance to ether stu dies that have investigated the effects of smoked marijuana on schedul e performance.