EFFECT OF REINFORCER MAGNITUDE ON PERFORMANCE MAINTAINED BY PROGRESSIVE-RATIO SCHEDULES

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 mu l. 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, 6, which defines it), minimum response time, increased as it function of reinforcer volume; the currency parameter, beta, 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 front 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.