Four rhesus monkeys were allowed water, which was continuously available on a fixed-ratio 1 (FR-1) schedule of reinforcement, and food, which was available on differing reinforcement schedules. In Exp. 1, water intake greatly increased when the food schedule was changed from continuous reinforcement to a variable-interval schedule. In Exp. 2, when the same schedule change was employed but the number of food reinforcements was held constant, the water intake increased as in Exp. 1. In Exp. 3, a fixed-ratio 25 (FR-25) schedule of food reinforcement was employed in which a total of approximately 80 food pellets were divided among 4, 8, 16, or 24 periods per 24-hr. session. Water intake was related linearly to the increase in the number of food periods. Since water responding took place only after the FR-25 food periods, it was argued that the schedule-induced polydipsia observed was not due to accidental chaining.
Pigeons’ preference for fixed-interval over fixed-ratio food reinforcement schedules
