Figure 2. Discounting functions.

(A) Exponential discounting reduces value by a fixed percentage over any time interval. Therefore the relative preference of two future rewards does not change as the time to these rewards approaches. (B) In hyperbolic discounting, a later/larger reward may be preferred over a sooner/smaller reward until the rewards draw closer, at which point choice preference can reverse so the sooner/smaller reward is impulsively preferred. After Ainslie [38], [41].