Schedules of differential reinforcement, especially when reinforcers depend on the temporal pacing of responses. Contingencies can be based on preceding interresponse times (IRTs), response rates during a preceding time, or periods of no responding either preceded by a response or without a required preceding response. They are usually arranged for free-operant responding, but also can be arranged within discrete trials. (Catania) In differential-reinforcement-of-long-interresponse times, differential-reinforcement-of-low-rate (DRL) or IRT > t schedules, a response is reinforced only if at least t seconds has elapsed since the last response. An alternative and less common method, based on rates rather than IRTS, reinforces a response only if fewer than n responses were emitted during the last t seconds. (Catania) In differential-reinforcement-of-high-rate (DRH) or IRT