Differential reinforcement of interresponse times with controlled probability of reinforcement per response

Pigeons were presented food after interresponse times (IRTs) longer or shorter than a fixed percentage of their most recent IRTs. This procedure controlled probability of reinforcement per response while still allowing different classes of IRTs to be reinforced differentially. Support was found for IRT-reinforcement theory in that response rates were determined by the degree and direction of differential reinforcement of IRTs, but were relatively independent of probability of reinforcement per response and of the length of the control system's IRT memory. Stimulus control of these differential response rates was also demonstrated.