Stafford, D., & Branch, M. N. (1998).
Effects of step size and break- point criterion on progressive-ratio performance.
Journal of the Experimental Analysis of Behavior,
70, 123-138.
Key pecking by pigeons was maintained by arithmetic
progressive-ratio schedules of food delivery. Successive
conditions arranged different step sizes, and each condition
remained in effect until behavior appeared stable. Each session
continued until a period of time passed in which no key pecks
were recorded (the break-point criterion); both a 5-min and a
15-min criterion were tested across a range of step sizes.
Average breaking points (i.e, the largest ratio completed) were
relatively unaffected by step-size magnitude, whereas the average
number of ratios completed and average response rates generally
declined across increasing step sizes. Within sessions, preratio
pauses were relatively short and fairly constant in duration as
the ratio increased; pause durations increased rapidly near the
end of a session. The relation between the average number of
completed ratios and step size was described well by a power
function [y = b(x[cf12]a), in which y
represents the average number of completed ratios, x
represents the step size, and a and b are fitted
parameters]. Increasing the break-point criterion from 5 to 15
min resulted in increased values of b, whereas parameter
a was relatively unaffected and was close to -1
(consistent with the lack of effect of step size on breaking
point). This function also provided an excellent description of
data drawn from previous reports.
Key words: progressive ratio, reinforcer efficacy, step size,
break-point criterion, key peck, pigeons