Acquisition and extinction in the presence of the same intertrial stimuli: The effects of partial reward

Two groups of rats (N = 11) were trained at two trials a day for 16 days in Phase I and 13 days in Phase II. Responses on Trial 1 were always rewarded in both phases. Percentage of reward (50% vs 100%) was varied on Trial 2 of each day of Phase I. Trial 2 on each day of Phase II was never rewarded. A partial reward effect (PRE) was observed on Trial 2 of Phase II. The implications of the results for intertrial explanations of the PRE were discussed.