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 th e partial reinforcement extinction effect (PREE). We report three experimen ts in which the extinction rates of random partially reinforced (PRF) or co ntinuously reinforced (CRF) infant rat pups were compared to the extinction rate of pups trained with an alternative and regular schedule of partial r einforcement, known as patterned single alternation of reward and nonreward trials in the straight alley runway. In Experiment 1, 17-day-old PSA subje cts showed CRF-like extinction rates; whereas in Experiment 2, in which ext inction was initiated early in training prior to the onset of the PSA discr imination, PSA subjects showed prolonged, PRF-like extinction curves. In co ntrast, 12-day-old pups in Experiment 3 showed no reward-schedule-related d ifferences in extinction, despite differences in behavior during acquisitio n. These results prompt a modification of Amsel's (1962) model of discrimin ation learning, and suggest the existence of a dissociation between differe nt types of reward-related expectancies in the younger subjects. (C) 1999 J ohn Wiley & Sons, Inc.