Foster, T. A., Hackenberg, T. D., & Vaidya, M. (2001). Second-order schedules of token reinforcement with pigeons: Effects of fixed- and variable-ratio exchange schedules. Journal of the Experimental Analysis of Behavior, 76, 159-178.

Pigeons' key pecks produced food under second-order schedules of token reinforcement, with light-emitting diodes serving as token reinforcers. In Experiment 1, tokens were earned according to a fixed-ratio 50 schedule and were exchanged for food according to either fixed-ratio or variable-ratio exchange schedules, with schedule type varied across conditions. In Experiment 2, schedule type was varied within sessions using a multiple schedule. In one component, tokens were earned according to a fixed-ratio 50 schedule and exchanged according to a variable-ratio schedule. In the other component, tokens were earned according to a variable-ratio 50 schedule and exchanged according to a fixed-ratio schedule. In both experiments, the number of responses per exchange was varied parametrically across conditions, ranging from 50 to 400 responses. Response rates decreased systematically with increases in the fixed-ratio exchange schedules, but were much less affected by changes in the variable-ratio exchange schedules. Response rates were consistently higher under variable-ratio exchange schedules than under comparable fixed-ratio exchange schedules, especially at higher exchange ratios. These response-rate differences were due both to greater preratio pausing and to lower local rates under the fixed-ratio exchange schedules. Local response rates increased with proximity to food under the higher fixed-ratio exchange schedules, indicative of discriminative control by the tokens.

Key words: fixed-ratio schedules, variable-ratio schedules, second-order schedules, token reinforcement, behavioral units, key peck, pigeons