The effects of delayed reinforcement on free-operant responding

In previous studies of delayed reinforcement, response rate has been found to vary inversely with the response-reinforcer interval. However, in all of these studies the independent variable, response-reinforcer time, was confounded with the number of reinforcers presented in a fixed period of time (reinforcer frequency). In the present study, the frequency of available reinforcers was held constant, while temporal separation between response and reinforcer was independently manipulated. A repeating time cycle, T, was divided into two alternating time periods, t(D) and t(Delta). The first response in t(D) was reinforced at the end of the prevailing T cycle and extinction prevailed in t(Delta). Two placements for t(D) were defined, an early t(D) placement in which t(D) precedes t(Delta) and a late t(D) placement in which t(D) follows t(Delta). The duration of the early and late t(D) was systematically decreased from 30 seconds (i.e., t(D) = T) to 0.1 second. Manipulation of t(D) placement and duration controlled the temporal separation between response and reinforcement, but it did not affect the frequency of programmed reinforcers, which was 1/T. The results show that early and late t(D) placements of equal duration have similar overall effects upon response rate, reinforcer frequency, responses per reinforcer, and obtained response-reinforcer temporal separation. A stepwise regression analysis using log response rate as the dependent variable showed that the obtained delay was a significant first-step variable for six of eight subjects, with obtained reinforcer frequency significant for the remaining two subjects.