Several different arrangements have been described for increasing the response requirements for reinforcement using the label "progressive-ratio schedule." Under the original progressive-ratio schedule, the response requirement is increased after each reinforcer. Subsequently, arrangements have been used in which the number of required responses…

This article reviews evidence from basic and translational research with pigeons and humans suggesting that the persistence of operant behavior depends on the contingency between stimuli and reinforcers, and considers some implications for clinical interventions. (Contains 4 figures.)