Schedule-induced drinking in humans: a potential factor in excessive alcohol use.

The timed delivery of monetary reinforcement by a computer-controlled slot machine altered the amount of fluid drunk adjunctively by human subjects. In separate experiments, subjects were allowed access to one of three fluids, water, non-alcoholic beer, or alcoholic beer, while receiving monetary reinforcement from the slot machine on one of two Fixed-Interval schedules (FI30 s or FI90 s). The largest difference in intake between the two schedule conditions occurred when water was the fluid available, but a similar trend in consumption was observed in the other studies. Greater consumption occurred when reinforcement was presented on the FI90-s schedule, which was predicted from previous studies using animals. The possible interaction of schedule-induced drinking with other variables known to influence human alcohol consumption is discussed.