DELAYED REWARD AND COST DISCOUNTING

28) chose between smaller, immediate and larger, delayed hypothetical monetary amounts in a cost and a reward condition. For both conditions, the choice procedure yielded equivalence points that measure the immediate amount reward or cost that is subjectively equivalent to the larger delayed reward or cost. Equivalence pOints from each of eight delays were used to estimate a discounting parameter for both hyperbolic and exponential discount functions. Hyperbolic functions accounted for more of the variance in both the reward and the cost condition, and delayed reward and cost discounting was significantly correlated. Participants discounted the value of delayed rewards to a greater degree than delayed costs. Previous research has found that substance abusers discount delayed rewards more than controls. Implications of the present findings for substance abuse and other health behaviors are discussed. People routinely choose between acts, the consequences of which may be positive and negative and immediate and delayed. For example, one may choose to turn off the alarm in the morning and sleep an extra 30 minutes. This would produce a relatively higher valued immediate outcome, but a relatively lower valued delayed outcome when one is late for work. Or, one could attend college rather than seek employment after high school. This would produce a relatively lower valued, lower income short-term future, but a relatively higher valued, higher income long-term future. Understanding how we choose between sooner and later rewards and costs has been an important task in psychological and economic research for some time (e.g., Ainslie, 1975; Kagel, Battalio, & Green, 1995; Mischel & Grusec, 1967; Rachlin, 1974). A key issue in understanding these choice situations has been describing the manner in which the value of rewards and costs varies as a function of delay (Kirby, 1997; Kirby