Stimulus- and pellet-induced drinking during a successive discrimination.

In three experiments, interim water drinking was examined in rats exposed to a multiple schedule whose two components were extinction and a variable-time 30-s schedule of food delivery. Two different drinking patterns were observed in Experiment 1. Pellet-induced drinking, characterized by high rates of postpellet drinking in the variable-time component, with little or no drinking in extinction, occurred when the acquisition of stable postpellet drinking preceded discrimination training. Stimulus-induced drinking, characterized by a burst of drinking at the onset of extinction, with no drinking during the variable-time schedule, occurred when discrimination training preceded all other experimental conditions. With extended training, stimulus-induced drinking eventually was accompanied by postpellet drinking. In Experiment 2, the rate of stimulus-induced drinking and the number of sessions during which it occurred without postpellet drinking were found to be inversely related to component duration. In Experiment 3, the rate of schedule-induced drinking was found to vary directly with component duration.