In this study, children, young adults, and older adults chose between immediate and delayed hypothetical monetary rewards. The amount of the delayed reward was held constant while its delay was varied. All three age groups showed delay discounting; that is, the amount of an immediate reward judged to be of equal value of the delayed reward decreased as a function of delay. The rate of discounting was highest for children and lowest for older adults, predicting a life-span developmental trend towards increased self-control. Discounting of delayed rewards by all three age groups was well described by a single function with age-sensitive parameters (all R²s > .94). Thus, even though there are quantitative age differences in delay discounting, the existence of an age-invariant form of discount function suggests that the process of choosing between rewards of different amounts and delays is quantitatively similar across the life span.
Abstract