Pairs of rats cooperate more when responding to simultaneous reinforcement than to alternated reinforcement

The purpose of this experiment was to explore whether simultaneous access to consequences configures a defining functional feature of coordination. We evaluated whether coordination episodes are maintained when reinforcers are alternately presented to two cooperating rats across these episodes, in contrast to the delivery of reinforcers simultaneously for both rats and independently for each rat. Rat pairs responded under either a tandem fixed-interval (FI) 10-s FI 10-s or a tandem variable-interval (VI) 10-s VI 10-s schedules. In the baseline, lever presses of each rat were individually reinforced according to the tandem FI FI schedule. In two simultaneous reinforcement conditions, reinforcer deliveries depended on coordination episodes under either tandem schedule. In two alternated reinforcement conditions, rats accessed reinforcers in alternation under either tandem schedule. Two main findings are reported: (1) proportions of coordination were consistently higher under the simultaneous than under the alternated reinforcement condition regardless of the type of tandem schedules (FI or VI) and (2) proportions of coordination were similar in the individual and alternated reinforcement conditions. Although the obtained reinforcement rates limit a conclusive evaluation, these findings indicate that the simultaneous delivery of reinforcers (mutual reinforcement) is a critical variable in the operant selection of coordinated responding.