Social Norms Shift Behavioral and Neural Responses to Foods

Abstract

Obesity contributes to 2.8 million deaths annually, making interventions to promote healthy eating critical. Although preliminary research suggests that social norms influence eating behavior, the underlying psychological and neural mechanisms of such conformity remain unexplored. We used fMRI to investigate whether group norms shift individuals' preferences for foods at both behavioral and neural levels. Hungry participants rated how much they wanted to eat a series of healthy and unhealthy foods and, after each trial, saw ratings that ostensibly represented their peers' preferences. This feedback was manipulated such that peers appeared to prefer each food more than, less than, or as much as participants themselves. After a delay, participants rerated each food. Participants' second ratings shifted to resemble group norms. Initial consensus, as compared to disagreement, with peers produced activity in the nucleus accumbens, a region associated with reward prediction errors. Furthermore, the strength of this activity predicted the extent to which participants' ratings conformed to peer ratings, suggesting that the value associated with consensus drives social influence. Ventromedial prefrontal cortex (vMPFC), a region associated with value computation, initially responded more strongly to unhealthy, as compared to healthy, foods. However, this effect was "overwritten" by group norms. After individuals learned their peers' preferences, vMPFC responses tracked the popularity, but not the healthfulness, of foods. Furthermore, changes in vMPFC activity tracked social influence over behavioral ratings. These data provide evidence that group norms can shift food preferences, supporting the use of norms-based interventions to promote healthy eating.

What’s in a word? How instructions, suggestions, and social information change pain and emotion

“…For instance, Zaki and colleagues (see also Campbell-Meiklejohn et al, 2010; Nook and Zaki, 2015; Zaki et al, 2011) first identified value- and reward-related brain areas (including ventral striatum, vmPFC, and OFC) using a monetary-incentive delay task. Similar to the Klucharev et al (2009) study, they then had male participants rate the attractiveness of female faces, and subsequently provided feedback about other people’s ratings.…”

Social Norms Shift Preferences for Healthy and Unhealthy Foods

“…To investigate this, we applied an analysis used in our prior work [22], as well as other recent conformity research [24]. We grouped each trial into one of three feedback bins: Peers Higher (25.8% of all trials), Peers Lower (31.4% of all trials), and Peers Same (42.8% of all trials).…”

“…First, this finding provides insight into how people update their preferences in response to social norm information. In our prior work, participants received social norm information about individual food items, irrespective of a norm rule [22]. There, participants updated their preferences on an item-by-item basis.…”

“…The present study addressed these limitations by adopting a paradigm we and others have used to study social influence [20–25], including over food preferences [22]. In this recent study, participants rated their preferences for healthy and unhealthy food images and then saw the average rating that previous participants ostensibly gave those same food images.…”

“…Participants then rated the same set of food images a second time, without viewing average ratings. During these second ratings, participants changed their food preferences to align with those of the group [22]. Crucially, though each participant rated both healthy and unhealthy images, peer ratings varied independently of the healthfulness of the stimuli.…”