Effects of variable and fixed second-order schedules on schedule-induced polydipsia in the rat.

Schedule-induced polydipsia was studied in rats on a variable second-order schedule in Experiments 1 and 2. Drinking occurred only following presentations of the pellet reinforcer and was not induced by a stimulus that was associated with pellet delivery. Moreover, it was shown that lever pressing for food was not competing with the opportunity to drink following the stimulus during non-reinforced intervals. In Experiment 3 a fixed second-order schedule was used, and only one animal drank following the presentation of the stimulus. A positive contrast effect was obtained with schedule-induced drinking in Experiments 1 and 2, and it was suggested that schedule-induced polydipsia shows behavioral interactions similar to those seen with food reinforced operants.