Discounting delayed and probabilistic rewards: Processes and traits

Discounting of delayed and probabilistic rewards was examined in two relatively large samples (Ns > 100). For both types of rewards, a hyperbola-like discounting function provided good fits to individual data. Amount of reward had opposite effects on temporal and probability discounting: Smaller delayed rewards were discounted more steeply than larger delayed rewards, whereas larger probabilistic rewards were discounted more steeply than smaller probabilistic rewards. The nonlinear scaling parameter of the hyperbola-like function was larger for larger probabilistic rewards, but did not vary with the amount of delayed reward. Taken together, these findings suggest that despite the similar form of the temporal and probability discounting functions, separate processes may underlie the discounting of delayed and probabilistic rewards. Finally, weak to moderate positive correlations were observed between the discounting of delayed and probabilistic rewards. This finding is inconsistent with the notion of an ‘‘impulsiveness’’ trait that links an inability to delay gratification with a tendency to gamble and take risks. 2003 Elsevier B.V. All rights reserved. PsycINFO classification: 2300; 3120 JEL classification: D81; D90