Schedule-induced drinking and reinforcement omission

Rats were given extended training on a fixed-interval one-minute schedule in the presence of freely available water. Each food pellet delivery was accompanied by brief stimuli of blackout and tone. A total of 10 probe test sessions was conducted after stability was obtained with a maximum of 9 within-session probes during each session. On probes brief stimuli, food, or both were omitted. Omitting brief stimuli, singularly or in combination, did not reliably affect licks or bar presses. Omitting food, in the presence or absence of brief stimuli, eliminated polydipsic rates of licking but rates of bar presses were low early in the interval if brief stimuli were present and high throughout the interval if brief stimuli were absent. These effects were similar to those obtained with second-order schedules and suggest that polydipsic levels of schedule-induced drinking are under the control of the discriminative properties of food reinforcers.