Neural mechanisms of social influence

The present investigation explores the neural mechanisms underlying the impact of social influence on preferences. We socially tagged symbols as valued or not – by exposing participants to the preferences of their peers – and assessed subsequent brain activity during an incidental processing task in which participants viewed popular, unpopular, and novel symbols. The medial prefrontal cortex (mPFC) differentiated between symbols that were and were not socially tagged – a possible index of normative influence – while aspects of the striatum (the caudate) differentiated between popular and unpopular symbols – a possible index of informational influence. These results suggest that integrating activity in these two brain regions may differentiate objects that have become valued as a result of social influence from those valued for non-social reasons. 2009 Elsevier Inc. All rights reserved. The iconic Lacoste green crocodile logo – initially created in others has become nearly axiomatic across the social sciences; the honor of the 1920s French tennis star Rene Lacoste – has waxed and waned in popularity over the years, enjoying enormous popularity in the United States in the late 1970s and early 1980s while nearly disappearing from sight in the 1990s, only to reemerge in this decade as a desired status symbol. One reason to buy clothing featuring this crocodile might be to emulate Lacoste himself, of course, but we would be surprised if American teenagers have any awareness of the origins of the logo. Instead, such trends are often driven by the adoption – and rejection – of products by others: The value of little green crocodiles depends critically on the value that others attach to that symbol. In this paper, we model the process by which social influence impacts preferences in a 1-h experimental session, using a paradigm in which we train participants to see symbols as socially valued or not by providing them with feedback about the preferences of others.We then examine the impact of this social feedback on the brain activity that participants exhibit while viewing objects that have been endorsed or rejected by their peers, exploring the neural processes underlying changes in valuation due to social influence. Mechanisms of social influence The notion that humans are influenced in their beliefs, preferences, and behaviors by the beliefs, preferences, and behaviors of ll rights reserved. ason). sheer number of terms used to describe this process is indicative of its ubiquity, from social influence to social proof to peer pressure to bandwagon effects to conformity to herding (Abrahamson, 1991; Asch, 1951; Banerjee, 1992; Bikhchandani, Hirshleifer, & Welch, 1992; see Cialdini & Goldstein, 2004; Sherif, 1936, for a review). Indeed, even non-human primates are quick to adhere to social norms (Whiten,Horner, & deWaal, 2005). The impact of social influence has been demonstrated in countless domains, including pain perception (Craig & Prkachin, 1978), littering (Cialdini, Reno, & Kallgren, 1990), voting (Gerber, Green, & Larimer, 2008), donating to charities (Reingen, 1982), expressing prejudice (Apfelbaum, Sommers, & Norton, 2008), choosing jobs (Higgins, 2001; Kilduff, 1990), investing in the stockmarket (Hong, Kubik, & Stein, 2004), and,most relevant to the current investigation, both adoption and rejection of consumer products (Berger & Heath, 2007). Judgment and decisionmaking researchers have also increasingly recognized the fundamental impact of social factors on human behavior: Investigations of such ‘‘social decision-making” (Sanfey, 2007) have the potential to speed the integration of psychologists with both neuroscientists and game theorists, offering a more complete account of human decision-making (Camerer, 2003). From an early stage in research exploring the effects of social factors on behavior, researchers focused their attention on a fundamental question: the extent to which behavior influenced by peers indicated a true change in attitude such that social influence changed people’s minds, or merely a desire to be publically consistent with the viewpoints of others. Following on Asch’s (1951) classic M.F. Mason et al. / Organizational Behavior and Human Decision Processes 110 (2009) 152–159 153 conformity studies, in which participants gave obviously wrong answers to a simple line judgment task when confederates had given those wrong answers before them, Deutsch and Gerard (1955) varied whether responses to such tasks were visible to others or not; they showed that conformity was at its highest when responses were public – due to what they termed normative influence – but that even responses given in private could be influenced by the behavior of others – what they termed informational influence. In this and subsequent investigations, the extent to which behavior was influenced by true changes in belief as opposed to public desires to conform was inferred by comparing behavior influenced only by private factors (anonymous behavior) from behavior influenced by both private and public factors; subtracting the former from the latter results in the amount of private attitude change. While this strategy is experimentally elegant, the ideal evidence for this theory would be to assess the underpinnings of normative and informational influence simultaneously. Brain imaging research offers just this potential. One of the key theoretical questions lingering from Asch’s initial investigation, for example, was whether participants were merely conforming to the confederate’s answers, or whether they came to literally see the wrong answers as correct. In a recent functional magnetic resonance imaging (fMRI) investigation of conformity in which confederates gave false answers to a mental rotation task, Berns et al. (2005) demonstrated that the erroneous responses of others altered activity in brain regions implicated in mental rotation, suggesting not just a social impact of conformity pressures, but a true change in perception (see Sherif, 1936). These results offer evidence that social influence can be indexed at the level of the brain, and suggest that examining different regions known to be implicated in different processes may be a fruitful avenue to examine two-factor theories of social influence. While the research reviewed above has focused primarily on conformity to tasks (line judgments and mental rotations), we use brain imaging to explore these dynamics in the domain of preferences, examining how the brain responds when participants are confronted by symbols that they previously learned were socially valued or socially rejected by others. In the spirit of previous studies on social influence, we consider both normative and informational aspects of such pressures, assessing brain activity in (a) regions involved with processing the opinions and mental states of others – the normative aspects of social influence and (b) regions implicated in experienced utility or reward – the informational aspects of social influence. Neural mechanisms of social influence