The present study investigated the effects of fixed-ratio (FR) and variable-ratio (VR) reinforcement schedules on patterns of cooperative responding in pairs of rats. Experiment 1 arranged FR 1, FR 10, and VR 10 schedules to establish cooperative responding (water delivery depended on the joint responding of two rats). Cooperative response rates and proportions were higher under intermittent schedules than under continuous reinforcement. The FR 10 schedule generated a break-and-run pattern, whereas the VR 10 schedule generated a relatively high and constant rate pattern. Experiment 2 evaluated the effects of parametric manipulations of FR and VR schedules on cooperative responding. Rates and proportions of cooperative responding generally increased between ratio sizes of 1 and 5 but showed no consistent trend as the ratio increased from 5 to 10. Experiment 3 contrasted cooperative responding between an FR6 schedule and a yoked control schedule. Coordinated behavior occurred at a higher rate under the former schedule. The present study showed that external consequences and the schedules under which the delivery of these consequences are based, select patterns of coordinated behavior.

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The effects of response-reinforcer relations on coordinated responding were investigated. Coordinated responding was defined as two lever presses, one by each rat that occurred within 500 ms of one another. Four conditions were arranged in an ABCB design. Coordinated responding was reinforced according to a fixed-ratio 6 (FR 6) schedule in Condition A. In Condition B, a response by each rat was required, independent of their temporal proximity, to produce water delivery under a variable-interval schedule. Condition C was a replication of Condition B, except that coordinated responding was required for reinforcer deliveries. All conditions involved simultaneous reinforcement, that is the rats received access to reinforcers at the same time. The results extended previous findings by demonstrating the requirement of coordinated responses to produce reinforcement affected both coordinated response rates and the proportion of such responses relative to the total responses in a session, in that both measures were higher in Conditions A and C than in Condition B. There also was control of the temporal distribution of coordinated responding by the type of schedule (FR or VI): A “break-and-run” pattern was observed under the FR schedule, and a constant response rate was observed under the VI schedule.

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