Reinforcement value of gustatory stimuli determined by progressive ratio performance

The progressive ratio schedule provides a means to determine reinforcement value that is independent of response rate. This is achieved by increasing the number of lever presses for each successive reinforcement until, eventually, the subject fails to respond within a designated time limit. The number of responses in the final completed ratio defines the break point. When tested with appetitive gustatory stimuli (sucrose and saccharin), rats showed a concentration-dependent increase in break point when food deprived (Experiment 1A and, for sucrose only, Experiments 1B and IC) but not when water deprived (Experiment 1A). For aversive gustatory stimuli (sodium chloride, citric acid, and quinine) break point declined as concentration increased (Experiment 1A). In Experiment 1C, reinforcement duration had a significant, although relatively small, influence on break point for each of three concentrations of sucrose. Experiment 2 found a dose-dependent effect of the neuroleptic drug haloperidol (0.025, 0.05, and 0.1 mg/kg) on break point for sucrose reinforcement. The present study demonstrates that the progressive ratio schedule provides a valuable method to assess the influence of manipulations that might affect the perceived reinforcement value of gustatory stimuli.