Collier, G. H., Hirsch, E. 1971. Reinforcing properties of spontaneous activity in the rat. Journal of Comparative and Physiological Psychology 77, 155-160.

Required 21 male sprague-dawley rats to bar press on an ascending sequence of fixed-ratio requirements in order to run in either a voluntary treadmill or a braked running wheel. In both testing situations the duration of the burst of running was controlled by the S. As the ratio requirement increased the amount of bar pressing increased, reinforcement density decreased, and the duration of the pause following reinforcement increased. These changes in instrumental behavior influenced both the amount and pattern of running. The level of running decreased with the ratio requirement but the average burst duration increased. It is concluded that increases in running that resulted from deprivation were due to changes in burst duration rather than instrumental performance.