Fixed-interval punishment.

The average rate of bar-pressing maintained by a variable-interval schedule of milk reinforcement in 33 rats was found to be a decreasing function of intensity of concurrent punishment and, over a wide range of shock intensities, was inversely related to punishment frequency. Cumulative records were, however, negatively accelerated during 30-min punishment sessions with complete suppression occurring earlier and earlier (after fewer and fewer shocks) as intensity increased. In addition, acceleration was often observed between successive fixed-interval shock presentations and, at low and moderate intensities, bursts of responding occurred after each shock. The time to recover between punishment sessions (post-punishment recovery) was an increasing monotonic function of punishment intensity.