Comparing extinction and contrast effects for operant wheel running and lever pressing on a multiple schedule

Extinction and positive contrast effects were assessed on a multiple schedule with lever pressing as the operant in one component and wheel running as the operant in the other component. FR 15 schedules produced 15% sucrose reinforcement in each component. Contrast for both operants was generated by placing responding in the alternate component on extinction. Results showed that extinction decreased and contrast increased both lever-pressing and wheel-running rates. However, the magnitude of the changes was greater for lever pressing. Extinction increased and contrast decreased postreinforcement pause (PRP) duration for lever pressing, but for wheel running, extinction decreased PRP duration while contrast did not change PRP duration. Finally, outcomes for lever pressing decreased with extinction and increased with contrast, but for wheel running, outcomes did not change with extinction and increased with contrast. These differences in contrast and extinction effects were explained by an automatic reinforcement effect generated by wheel-running, but not lever pressing. These findings provide further support for an automatic reinforcement effect generated by wheel running.