EFFECTS OF STEP-SIZE AND BREAK-POINT CRITERION ON PROGRESSIVE-RATIO PERFORMANCE

Key pecking by pigeons was maintained by arithmetic progressive-ratio schedules of food delivery. Successive conditions arranged different s tep sizes, and each condition remained in effect until behavior appear ed stable. Each session continued until a period of time passed in whi ch no key pecks were recorded (the break-point criterion); both a 5-mi n and a 15-min criterion were tested across a range of step sizes. Ave rage breaking points (i.e, the largest ratio completed) were relativel y unaffected by step-size magnitude, whereas the average number of rat ios completed and average response rates generally declined across inc reasing step sizes. Within sessions, preratio pauses were relatively s hort and fairly constant in duration as the ratio increased; pause dur ations increased rapidly near the end of a session. The relation betwe en the average number of completed ratios and step size was described well by a power function [y = b(x(a)), in which y represents the avera ge number of completed ratios, x represents the step size, and a and b are fitted parameters]. Increasing the break-point criterion from 5 t o 15 min resulted in increased values of b, whereas parameter a was re latively unaffected and was close to -1 (consistent with the lack of e ffect of step size on breaking point). This function also provided an excellent description of data drawn from previous reports.