Effects of the Permutation of Reinforcement Magnitude on Measures of Delay Discounting in a Hypothetical Money Scenario

Abstract

The current study analyzed the extent to which three common permutations of reinforcement magnitude – quantity, volume, and duration – affected the rate at which participants discounted hypothetical monetary rewards. College students served as participants. Hypothetical scenarios were presented using the Hypothetical Money Procedure (Kirby, 1996), and participants self-reported the subjective value of a delayed monetary reward. Conditions presented the monetary choices as (a) quantity of dollar bills, (b) heights (inches) of a stack of dollar bills, and (c) durations of time to spend in a hypothetical cash machine to collect dollar bills. For each condition, participants’ combined subjective values were used to calculate area under the curve (AuC) and to generate discounting curves based on Mazur’s (1987) hyperbolic model. The duration permutation yielded a statistically significant smaller AuC value and resulted in a higher k-value in comparison to the quantity and volume permutations. Response patterns also were used to group participants based on the permutation that yielded the highest idiosyncratic AuC value. The permutation of reinforcement magnitude was demonstrated to be a significant variable in controlling discounting rates for hypothetical money.