Is extinction the hallmark of operant discrimination?: :: Reinforcement and SΔ effects

Using a successive discrimination procedure with rats, three experiments investigated the contribution of reinforcement rate and amount of S' exposure on the acquisition of an operant discrimination. S-D components and were always 2 min in length, while S-D (extinction) components were either 1 min or 4 min in length; responses in S-D were reinforced on one of four schedules. In Experiment 1, each of eight groups were exposed to one possible combination of rate of reinforcement and S-Delta component length. At every level of reinforcement, the 4 min S-Delta groups acquired the discrimination more quickly. However, within each level of reinforcement, the proportions of responding in SD as a function cumulative S-Delta exposure were equivalent, regardless of the number of reinforcers earned in So, suggesting that extinction is the "hallmark" of discrimination. Experiment 2 sought to replicate these results in a within-subjects design, and although the 4 min S-D conditions always produced superior discriminations, the lack of discriminated responding in some conditions suggested that stimulus disparity was reduced. Experiment 3 clarified those results and extended the finding that the acquisition of operant discrimination closely parallels extinction of responding in S'. In sum, it appears that higher reinforcement rates and longer S-Delta exposure facilitate the acquisition of discriminated operant responding. (c) 2006 Elsevier B.V. All rights reserved.