The time from a response to a later reinforcer. Reinforcers usually lose effectiveness as delay increases, but properties of delay procedures complicate the determination of the delay-of-reinforcement function. In delay procedures that interpose a stimulus between the response and its delayed reinforcer (signaled delay of reinforcement), the stimulus probably functions as an immediate conditioned reinforcer. In procedures that interpose no stimulus, either the delay is extended by additional responses, thereby limiting response rate because a reinforcer is delivered only after a pause equal to the delay interval, or the delay is unaffected by additional responses, thereby allowing the delay to be effectively reduced to the shorter time between those responses and the reinforcer at the end of the delay.