Is extinction the hallmark of operant discrimination? Reinforcement and S(Delta) effects

Using a successive discrimination procedure with rats, three experiments investigated the contribution of reinforcement rate and amount of S(Delta) exposure on the acquisition of an operant discrimination. S(D) components and were always 2 min in length, while S(Delta) (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 S(D) as a function cumulative S(Delta) exposure were equivalent, regardless of the number of reinforcers earned in S(D), 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(Delta) 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(Delta). In sum, it appears that higher reinforcement rates and longer S(Delta) exposure facilitate the acquisition of discriminated operant responding.