PAST EXPERIENCE, RECENCY, AND SPONTANEOUS-RECOVERY IN CHOICE BEHAVIOR

Pigeons' responses on two keys were recorded before and after the perc entage of reinforcers delivered by each key was changed. In each condi tion of Experiment 1, the reinforcement percentage for one key was 50% for several sessions, then either 70% or 90% for one, two, or three s essions, and then 50% for another few sessions. At the start of the se cond and third sessions after a change in reinforcement percentages, c hoice percentages often exhibited spontaneous recovery-a reversion to the response percentages of earlier sessions. The spontaneous recovery consisted of a shift toward a more extreme response percentage in som e cases and toward a less extreme response percentage in other cases, depending on what reinforcement percentages were previously in effect. In Experiment 2, some conditions included a 3-day rest period before a change in reinforcement percentages, and other conditions included n o such rest days. Slightly less spontaneous recovery was observed in c onditions with the rest periods, suggesting that the influence of prio r sessions diminished with the passage of time. The results are consis tent with the view that choice behavior at the start of a new session is based on a weighted average of the events of the past several sessi ons.