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Many important decisions involve outcomes that are either probabilistic or delayed. Based on similarities in decision preferences, models of decision making have postulated that the same psychological processes may underlie decisions involving probabilities (i.e., risky choice) and decisions involving delay (i.e., intertemporal choice). Equivocal behavioral evidence has made this hypothesis difficult to evaluate. However, a combination of functional neuroimaging and behavioral data may allow identification of differences between these forms of decision making. Here, we used functional magnetic resonance imaging (fMRI) to examine brain activation in subjects making a series of choices between pairs of real monetary rewards that differed either in their relative risk or their relative delay. While both sorts of choices evoked activation in brain systems previously implicated in executive control, we observed clear distinctions between these forms of decision making. Notably, choices involving risk evoked greater activation in posterior parietal and lateral prefrontal cortices, whereas choices involving delay evoked greater activation in the posterior cingulate cortex and the striatum. Moreover, activation of regions associated with reward evaluation predicted choices of a more-risky option, whereas activation of control regions predicted choices of more-delayed or less-risky options. These results indicate that there are differences in the patterns of brain activation evoked by risky and intertemporal choices, suggesting that the two domains utilize at least partially distinct sets of cognitive processes.

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Some decisions involve uncertain outcomes. For example, selecting an entrée at a restaurant entails uncertainty about how delicious each menu option would be. Other decisions involve delayed outcomes. For example, initiating an exercise program entails a delay until the positive results of exercise are observed. Both decision making under uncertainty and intertemporal choice have been the topic of much research. In the present article, we analyze potential parallels between these two types of choices.Decision making under uncertainty can be characterized by risk preferences. A preference for a lottery over its expected value (EV) (e.g., preferring a 50% chance of $10 over $5 for sure) is considered risk seeking, whereas a preference for the expected value over the lottery (e.g., preferring the $5 for sure) is known as risk aversion. Intertemporal choice can be characterized by time preferences. A preference for a positive outcome now rather than for an equivalent outcome later (e.g., preferring $10 now to $10 in 1 month) is called a positive time preference, and the extent of the time preference can be quantified as a discount rate, or the percentage of increase in the magnitude of the payout needed to offset a delay. For example, a 20% monthly discount rate would mean that $10 now is equally preferable to $12 in 1 month (Frederick, Loewenstein, & O'Donoghue, 2003).There are apparent parallels between choice under uncertainty and intertemporal choice-that is, seemingly analogous phenomena that could be explained if risk preferences and time preferences are driven by common factors (see Green & Myerson, 2004). A number of researchers have suggested that time and delay are parallel (e.g., Keren & Roelofsma, 1995;Rachlin, Logue, Gibbon, & Frankel, 1986) or have analogous effects on choice (Chapman, 1997;Gafni & Torrance, 1984;Myerson, Green, Hanson, Holt, & Estle, 2003).The study of both choice under uncertainty and intertemporal choice has centered around the analysis of decision biases, or deviations from normative theory. Risky choice biases are deviations from expected utility theory (Neumann & Morgenstern, 1953). Intertemporal choice biases are deviations from discounted utility theory (Koopsman, 1960). Prelec and Loewenstein (1991;Loewenstein & Prelec, 1992) noted that some risky choice biases parallel intertemporal choice biases.The purpose of the present experiments was to provide an empirical test of a particular account of the apparent parallels between biases in risky choice and biases in intertemporal choice. That is, we tested the idea that biases in the two domains that appear similar are the result of the same underlying mechanism. We first will describe two pairs of biases; we then will present a psychophysical account for parallels between the biases and, finally, an empirical test devised to evaluate this account. Pairs of Parallel BiasesCommon difference and common ratio effects. The common difference effect is a bias in intertemporal choice in which adding a constant delay to both choice op- Two...