NONSTABLE CONCURRENT CHOICE IN PIGEONS

Six pigeons were trained on concurrent variable-interval schedules in which the arranged reinforcer ratios changed from session to session a ccording to a 31-step pseudorandom binary sequence. This procedure all ows a quantitative analysis of the degree to which performance in an e xperimental session is affected by conditions in previous sessions. Tw o experiments were carried out. In each, the size of the reinforcer ra tios arranged between the two concurrent schedules was varied between 31-step conditions. In Experiment 1, the concurrent schedules were arr anged independently, and in Experiment 2 they were arranged nonindepen dently. An extended form of the generalized matching law described the relative contribution of past and present events to present-session b ehavior. Total performance in sessions was mostly determined by the re inforcer ratio in that session and partially by reinforcers that had b een obtained in previous sessions. However the initial exposure to the random sequence produced a lower sensitivity to current-session reinf orcers but no difference in overall sensitivity to reinforcement. Ther e was no evidence that the size of the reinforcer ratios available on the concurrent schedules affected either overall sensitivity to reinfo rcement or the sensitivity to reinforcement in the current session. Th ere was also no evidence of any different performance between independ ent and nonindependent scheduling. Because of these invariances, this experiment validates the use of the pseudorandom sequence for the fast determination of sensitivity to reinforcement.