Ricard, J.F.,Body, S., Zhang, Z.,Bradshaw, C.M. & Szabadi, E. (2009).
Effect of reinforcer magnitude on performance maintained by progressive-ratio schedules.
Journal of the Experimental Analysis of Behavior, 91, 75-87.
This experiment examined the relationship between reinforcer magnitude and quantitative measures of performance on progressive-ratio schedules. Fifteen
rats were trained under a progressive-ratio schedule in seven phases of the experiment in which the volume of a 0.6-M sucrose solution reinforcer was
varied within the range 6-300 µl. Overall response rates in successive ratios conformed to a bitonic equation derived from Killeen’s (1994) Mathematical
Principles of Reinforcement. The “specific activation” parameter, a, which is presumed to reflect the incentive value of the reinforcer, was a
monotonically increasing function of reinforcer volume; the “response time” parameter, ð, which defines the minimum response time, increased as a
function of reinforcer volume; the “currency” parameter, ß, which is presumed to reflect the coupling of responses to the reinforcer, declined as a
function of volume. Running response rate (response rate calculated after exclusion of the postreinforcement pause) decayed monotonically as a function
of ratio size; the index of curvature of this function increased as a function of reinforcer volume. Postreinforcement pause increased as a function of
ratio size. Estimates of a derived from overall response rates and postreinforcement pauses showed a modest positive correlation across conditions and
between animals. Implications of the results for the quantification of reinforcer value and for the use of progressive-ratio schedules in behavioral
neuroscience are discussed..
Key words: progressive-ratio schedule, reinforcer magnitude, Mathematical Principles of Reinforcement (MPR), lever press, rat