Cognitive flexibility refers to various processes which enable behaviors to be modified on the basis of a change in the contingencies between stimuli or responses and their associated outcomes. Reversal learning is a form of cognitive flexibility which measures the ability to adjust responding based on a switch in the stimulus--outcome…

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…