Separation of time-based and trial-based accounts of the partial reinforcement extinction effect

Abstract

Two appetitive conditioning experiments with rats examined time-based and trial-based accounts of the partial reinforcement extinction effect (PREE). In the PREE, the loss of responding that occurs in extinction is slower when the conditioned stimulus (CS) has been paired with a reinforcer on some of its presentations (partially reinforced) instead of every presentation (continuously reinforced). According to a time-based or "time-accumulation" view (e.g., Gallistel and Gibbon, 2000), the PREE occurs because the organism has learned in partial reinforcement to expect the reinforcer after a larger amount of time has accumulated in the CS over trials. In contrast, according to a trial-based view (e.g., Capaldi, 1967), the PREE occurs because the organism has learned in partial reinforcement to expect the reinforcer after a larger number of CS presentations. Experiment 1 used a procedure that equated partially and continuously reinforced groups on their expected times to reinforcement during conditioning. A PREE was still observed. Experiment 2 then used an extinction procedure that allowed time in the CS and the number of trials to accumulate differentially through extinction. The PREE was still evident when responding was examined as a function of expected time units to the reinforcer, but was eliminated when responding was examined as a function of expected trial units to the reinforcer. There was no evidence that the animal responded according to the ratio of time accumulated during the CS in extinction over the time in the CS expected before the reinforcer. The results thus favor a trial-based account over a time-based account of extinction and the PREE. This article is part of a Special Issue entitled: Associative and Temporal Learning.

Keywords: Associative models; Extinction; Partial reinforcement extinction effect; Timing models.

Figure 1

Mean elevation scores of the groups during each session of the conditioning phase of Experiment 1. PRF = partial reinforcement; CRF = continuous reinforcement; numbers before and after hyphens in the group designations give CS duration during conditioning and extinction, respectively.

Figure 2

Mean elevation scores of the groups during the extinction phase of Experiment 1. PRF = partial reinforcement; CRF = continuous reinforcement; numbers before and after hyphens in the group designations give CS duration during conditioning and extinction, respectively.

Figure 3

The extinction procedure used in Experiment 2. Trial durations alternated between 30-s and 10-s. Top: Time units when the PRF and CRF groups should have expected the US are indicated by arrows (40s and 10 s for the groups, respectively). The lines connect units where the PRF and CRF groups had equal ratios of accumulated time in the CS / expected time to the US. Bottom: Trial units where the PRF and CRF groups should have expected the US are indicated by arrows (every 4^th trial and every trial, respectively). The lines connect units where the PRF and CRF groups had equivalent trial expectancies. See text for more explanation.

Figure 4

Mean elevation scores of the groups during the conditioning phase of Experiment 2. PRF = partial reinforcement; CRF = continuous reinforcement.

Figure 5

Mean elevation scores of the groups over 4-trial blocks during the entire extinction phase of Experiment 2. PRF = partial reinforcement during acquisition; CRF = continuous reinforcement during acquisition.

Figure 6

Mean elevation scores of the partially-reinforced group (PRF) and continuously-reinforced group (CRF) in the extinction phase of Experiment 2 as a function time units (upper panel) and trial units (lower panel) expected to reinforcement.

Figure 7

Mean number of two-trial blocks required for the partially-reinforced (PRF) and continuously-reinforced (CRF) groups to reach the extinction criterion when trials were blocked in terms of time units (left) and trial units (right) expected to reinforcement in Experiment 2.