Local Response Rates on Variable-Ratio Schedules of Wheel-Running Reinforcement are Relatively Invariant Compared to Sucrose

Responding on variable-ratio (VR) schedules of wheel-running and sucrose reinforcement was assessed using a within-session procedure. Six female Long Evans rats were exposed to schedules ranging from VR 3 to VR 40 in ascending and descending order within a session with sucrose (0.1 ml of 15 % solution) and wheel-running reinforcement (30 s). Within a session, 10 reinforcers were obtained on each schedule, with a 120 s inter-component interval between schedules. Results showed that local response rates generated by sucrose were higher and that the pattern of local response rates across the schedules differed substantively between reinforcer types. With sucrose, local rates decreased linearly as the ratio requirement increased. With wheel running, local rates did not differ except to decline on the highest ratio. Post-reinforcement pauses were longer with wheel-running reinforcement and longer on the highest ratio when this ratio occurred at the end of a session. In contrast, wheel-running rates were lower on the smallest ratio schedule when this schedule occurred at the beginning of a session. The implications of the marked difference in local response rates across these schedules were discussed.