Effects of response effort on self-control in rats

Five rats served as subjects in an experiment that examined the effect of increasing response effort on self-control (choice of a larger, more delayed reinforcer over a smaller, less delayed reinforcer). The rats made significantly more self-control choices as the force required to respond on each lever increased from 0.1 to 0.8 N. As the force required to press the levers increased to 1 N and then began to decrease, some of the rats stopped responding. For those rats that continued to respond, self-control tended to decrease. The results suggest that increasing the required response force can increase self-control choices, as long as the required response force is low enough that some responding occurs.