Preference for Fairness Activates Reward Circuitry (and Disregarding Unfairness Activates Self-Control Circuitry)

Little is known about the positive emotional impact of fairness or the process of resolving conflict between fairness and financial interests. In past research, fairness has covaried with monetary payoff, such that the mental processes underlying preference for fairness and those underlying preference for greater monetary outcome could not be distinguished.We examined self-reported happiness and neural responses to fair and unfair offers while controlling for monetary payoff. Compared with unfair offers of equal monetary value, fair offers led to higher happiness ratings and activation in several reward regions of the brain. Furthermore, the tendency to accept unfair proposals was associated with increased activity in right ventrolateral prefrontal cortex, a region involved in emotion regulation, andwith decreased activity in the anterior insula, which has been implicated in negative affect. This work provides evidence that fairness is hedonically valued and that tolerating unfair treatment for material gain involves a pattern of activation resembling suppression of negative affect. Anyone who has watched children negotiate how to share a piece of cake knows that humans are exquisitely sensitive to fairness. Although economic models of decision making have traditionally assumed that individuals are motivated solely by material utility (e.g., financial payouts) and are not directly affected by social factors such as fairness (Camerer, Loewenstein, & Prelec, 2005; Kahneman, Knetsch, & Thaler, 1986), there is increasing empirical evidence that fairness does play a role in economic decision making (Fehr & Schmidt, 1999; Sears & Funk, 1991). Fairness in economic-exchange tasks is typically defined as the equitable distribution of an initial stake of money between two people. Because fair outcomes tend to be more materially desirable for the recipient than unfair outcomes in everyday life, it is difficult to distinguish the desire for fairness from the desire for material gain. Bilateral bargaining games, such as the ultimatum game, allow these two potential motives to be examined separately. The results of studies using the ultimatum game indicate that people are sensitive to fairness over and above its consequences for material gain (Güth, Schmittberger, & Schwarze, 1982). Although there is evidence that receiving an unfair proposal is associated with negative emotional responses (Sanfey, Rilling, Aronson, Nystrom, & Cohen, 2003), no study on economic decision making has examined whether a fair proposal produces positive emotional responses beyond those associated with the material gain itself. To examine the emotional response associated with fair treatment, we conducted two ultimatum-game experiments. In this game, one player proposes how to split a given sum ofmoney, the stake, and another player responds. If the responder accepts, each player keeps the amount allocated by the proposer. If the responder rejects the offer, neither player receives any money. Numerous studies using the ultimatum game have shown that responders do not maximize material utility by accepting every offer, but rather tend to reject offers below 20% of the stake (Camerer & Thaler, 1995), even when there will be no future interactions with the partner (Güth et al., 1982). In a neuroimaging study of the ultimatum game, Sanfey et al. (2003) observed that being treated unfairly is associated with a negative emotional response, inferred from anterior insula activation. They did not report what regions were more active during fair than during unfair offers. Furthermore, because fair offers (i.e., $5 out of $10) were always associated with higher monetary payoff than unfair offers (e.g., $2 out of $10), it is difficult to dissociate emotional response to fairness from emotional response to monetary payoff in their study. Hence, it is unclear from these data whether fair treatment is rewarding, in addition to unfair treatment being aversive. Research on social justice suggests that seeking justice is a basic human impulse (i.e., the justice motive; Tyler, 1991), possibly rooted in a basic social motivation to be accepted (BauAddress correspondence to Golnaz Tabibnia, The Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, 760 Westwood Plaza, C8-532, Los Angeles, CA 90095-1759, e-mail: [email protected]. PSYCHOLOGICAL SCIENCE Volume 19—Number 4 339 Copyright r 2008 Association for Psychological Science meister & Leary, 1995). Perceived fair treatment from public institutions (e.g., court, police) has been associated with satisfaction beyond the effects of the material outcomes, such as sentencing (Tyler, 1984). Critically, studies examining the impact of fairness on positive and negative emotions separately, controlling for material outcomes, have found substantial increases in self-rated positive emotions associated with fair treatment (De Cremer & Alberts, 2004; Hegtvedt & Killian, 1999). If being treated fairly is experienced as rewarding, then people should be happier with a fair offer than with an unfair offer of the same monetary value. Similarly, brain regions associated with reward should be more active during fair than during unfair treatment, after controlling for material utility. These reward regions include the ventral striatum, the amygdala, ventromedial prefrontal cortex (VMPFC), orbitofrontal cortex (OFC), and midbrain dopamine regions (Cardinal, Parkinson, Hall, & Everitt, 2002; Trepel, Fox, & Poldrack, 2005). Although the amygdala has commonly been associated with fear processes, activity in this structure, particularly on the left, has also been associated with reward processes (Hommer et al., 2003; Zalla et al., 2000). In order to control for material utility, we varied both the offer amount and the stake size across trials (see Fig. 1). On different trials, the same offer amount could represent a large percentage of the total stake (e.g., $7 out of $15), and therefore seem fair, or a small percentage of the total stake (e.g., $7 out of $23), and therefore seem unfair. Differences in ratings of happiness or reward activations observed in the comparison of such trials cannot be attributed to the magnitude of the monetary reward and thus are reasonably attributed to fairness. We also examined neural response during trials in which fairness and material outcome were at odds—that is, trials on which the offers were unfair but financially desirable (e.g., $8 out of $23). Thus, we examined the neural correlates of the tendency to accept unfair offers. Two possibilities were investigated. First, accepted unfair offers may activate reward circuitry to a greater extent than rejected unfair offers; such a pattern would reflect enhanced desire to accept the offers. Second, emotion regulation may be engaged when unfair offers are accepted, which would diminish the anterior insula’s response and decrease the desire to reject the offer. In this case, one would expect decreased activity in the anterior insula and increased activity in a prefrontal region that has been associated with emotion regulation, such as the right ventrolateral prefrontal cortex (right VLPFC; Hariri, Bookheimer, & Mazziotta, 2000; Lieberman et al., 2007). Participants in our studies played the role of responder. In Experiment 1, wemeasured emotional responses to each offer by obtaining self-ratings of happiness and contempt. In Experiment 2, we measured neural responses to fair and unfair offers using functional magnetic resonance imaging (fMRI). Participants were told that their decisions regarding four randomly selected offers in the experiment would actually be implemented, such that they and the proposers of those offers would be paid or not, according to the responses.