Fig. 3.

Effects of repeated cycles of 5-day access to Chow A/I alternated by 2-day access to either Chow A/I (Chow A/I / Chow A/I, n = 14) or highly preferred chocolate-flavored sugary diet (Chow A/I / Preferred, n = 15) on the time course by which 45-mg Chow A/I pellet reinforcers were obtained by male Wistar rats under a progressive ratio schedule of reinforcement. Testing occurred on the first day of the Chow A/I (C) phase of week 5. Values are presented as means ± SE. *Significantly different from Chow A/I / Chow A/I, P < 0.05, ***P < 0.001. The rate at which subjects earned reinforcers per unit time is shown. Each symbol represents the mean number of cumulative reinforcers earned by subjects through that time point. The time course is continued until each subject in the group has stopped obtaining reinforcers, and the graph therefore does not represent average session durations.