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 SΔ exposure on the acquisition of an operant discrimination. SD components and were always 2 min in length, while SΔ (extinction) components were either 1 min or 4 min in length; responses in SD 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 SΔ component length. At every level of reinforcement, the 4 min SΔ groups acquired the discrimination more quickly. However, within each level of reinforcement, the proportions of responding in SD as a function cumulative SΔ exposure were equivalent, regardless of the number of reinforcers earned in SD, 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 SΔ 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 SΔ. In sum, it appears that higher reinforcement rates and longer SΔ exposure facilitate the acquisition of discriminated operant responding.