Extinction after regular and irregular reward schedules in the infant rat: influence of age and training duration.

Greater persistence in extinction is observed following inconsistent reward compared to that observed following consistent reward, an effect termed the partial reinforcement extinction effect (PREE). We report three experiments in which the extinction rates of random partially reinforced (PRF) or continuously reinforced (CRF) infant rat pups were compared to the extinction rate of pups trained with an alternative and regular schedule of partial reinforcement, known as patterned single alternation (PSA). In PSA, subjects learn to alternate speed of responding in anticipation of the regular alternation of reward and nonreward trials in the straight alley runway. In Experiment 1, 17-day-old PSA subjects showed CRF-like extinction rates; whereas in Experiment 2, in which extinction was initiated early in training prior to the onset of the PSA discrimination, PSA subjects showed prolonged, PRF-like extinction curves. In contrast, 12-day-old pups in Experiment 3 showed no reward-schedule-related differences in extinction, despite differences in behavior during acquisition. These results prompt a modification of Amsel's (1962) model of discrimination learning, and suggest the existence of a dissociation between different types of reward-related expectancies in the younger subjects.