Choice behavior in pigeons maintained with probabilistic schedules of reinforcement

Pigeons were trained in three experiments with a two-key, concurrent-chains choice procedure. The initial links were equal variable-interval schedules, and the terminal links were random-time schedules with equal average interreinforcement intervals. Across the three experiments, the pigeons either stayed in a terminal link until a reinforcer was delivered or were returned to the initial links if a reinforcer was not delivered after the first unit time interval. The results showed that choice responding in concurrent chains is a complex function of (a) local factors, such as the immediacy of reinforcement in a terminal link, and (b) overall factors, such as the overall interreinforcement interval as calculated over both initial and terminal links of the chain. However, the local factors are generally stronger when the two factors are directly opposed.