INVESTIGATION OF THE COGNITIVE PROCESSES UNDERLYING SOCIAL CHOICES

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Social motivation as cooperative strategy

Human beings’ social motivation is self-evident in cognitive science and countless papers state in their opening lines that ‘humans are a highly social species’. While many non-human animals live in groups and interact with conspecifics, Homo sapiens are indeed exceptional in the variety of social interactions they pursue (Kaplan et al., 2009). For humans, social interactions are indeed frequent, diverse and rewarding (Hayden, Parikh, Deaner, & Platt, 2007; Izuma, Saito, & Sadato, 2008; O’Doherty et al., 2003; Pfeiffer et al., 2014; Rademacher et al., 2010; Ruff & Fehr, 2014). Social stimuli such as faces and speech are granted special attention from birth (Salva, Farroni, Regolin, Vallortigara, & Johnson, 2011; Vouloumanos, Hauser, Werker, & Martin, 2010) and interactive activities are consistently favored over solitary ones by children as young as three (Rekers, Haun, & Tomasello, 2011). In adults, social cues receive attentional priority (Langton, Law, Burton, & Schweinberger, 2008; Lavie, Ro, & Russell, 2003; Ro, Friggel, & Lavie, 2007) and positive social feedback reinforces learning (Chevallier et al., 2016; Jones et al., 2011; A. Lin, Adolphs, & Rangel, 2012- see Appendix). By contrast, ostracism and social rejection are experienced as painful (DeWall & Bushman, 2011; Eisenberger, Lieberman, & Williams, 2003; Kross, Berman, Mischel, Smith, & Wager, 2011) and can trigger intense negative psychological states (Cacioppo & Hawkley, 2009). Strikingly, Epley and Schroeder (2014) demonstrated that even when participants predict that they would prefer social isolation over social interaction, the precise opposite happens. Even when forced then, social interactions are rewarding.
Recently, it has been proposed that social motivation can be construed as an adaptation to collaborative environments, which are characterized by a strong reliance on cooperation to access resources (Chevallier, Kohls, et al., 2012). In this perspective, social motivation would be a coordinated strategy to motivate individuals to take part in collaborative interactions and to allocate enough attention and resources to prevent the fitness costs associated with cooperation, such as being exploited or left alone. This theory predicts that the more people are socially motivated, the more they should care about others’ reliability – to avoid being exploited – and the more they should care about their reputation – to avoid being shunned. In line with this idea, individuals who score high on a measure of social motivation (the social desirability scale) are also more concerned with their reputation and give more to charities as a result (Satow, 1975). On the opposite side of the spectrum, individuals who have diminished social motivation, such as people on the Autism Spectrum Disorder, are less concerned with their reputation (Begeer et al., 2008; Cage, Pellicano, Shah, & Bird, 2013; Chevallier et al., 2014; Chevallier, Grèzes, Molesworth, Berthoz, & Happé, 2012; Izuma, Matsumoto, Camerer, & Adolphs, 2011; Scheeren, Begeer, Banerjee, Terwogt, & Koot, 2010). In the same way, this theory predicts that social motivation should also be associated with differences in approach-avoidance behavior. More precisely, according to this theory, highly socially motivated individuals should grant more importance to cooperation-related than to power-related signals to decide who to approach and who to avoid.
To test this hypothesis, we investigated individual differences in the weight granted to cooperation- and power-related signals in face evaluation in a total sample of 410 participants tested across three experiments with direct replications. We found that social motivation is robustly associated with specific differences in the way power- and cooperation-related signals are combined to produce approach-avoidance judgments. We then modeled participants’ decisions in a trustworthiness-dominance two-dimensional space and found that highly socially motivated individuals are ready to approach a wider spectrum of trustworthy partners, which may be identified as a high-stake cooperative strategy relying on a widening of the cooperation circle to more powerful partners. Our results thus confirmed the link between higher social motivation and higher importance granted to cooperation-related cues predicted by the evolutionary model of social motivation and refined the hypothesis about the cooperative strategy associated with social motivation (Chevallier, Kohls, et al., 2012).
My contribution to this work was as follows: design of the experiment, collection and analysis of the data, and writing of the paper. The manuscript in which the results are reported has been submitted to Nature Human Behavior.

Abstract

That humans belong to a highly social species is hardly debated and it is now well-established that being motivated to form solid social bonds enhances fitness across multiple mammal species. Yet, the proximate mechanisms by which such social motivation promotes success in the human ecological niche are mostly underspecified. Here, we demonstrate across five experiments that social motivation is robustly associated with a targeted increase in the weight granted to cooperation-related cues to produce approach-avoidance decisions. Modeling participants’ decisions further revealed that motivation for social bonding results in a high-risk / high-reward cooperative strategy relying on a widening of the cooperation circle to include more powerful partners.

Significance statement

The motivation to form social bonds is widely regarded as a fitness enhancing feature in social species. Yet, initiating social interactions also brings about a range of risks. Here we test the hypothesis that increased motivation for social bonding comes with a targeted increased in people’s sensitivity to cooperation-related cues, which protects individuals from exploitation risks. High social motivation does not lead individuals to approach more partners indiscriminately; rather, motivation for social bonding is associated with a high-risk / high-reward cooperation strategy involving interactions with more powerful partners.

Main text

While many non-human animals live in groups and interact with conspecifics, Homo sapiens are exceptional in the variety of social interactions they pursue1. For humans, social interactions are indeed frequent, diverse and rewarding2–8. Individuals are biased to seek positive social interactions and maintain social bonds9–13. There is now a consensus on the fact that the motivation to form social bonds plays a key role in human behaviour and enhances individual fitness8,14,15. However, beyond the fitness advantage conferred by successful and stable social bonds16, the mechanisms by which social motivation ultimately promote success in the human ecological niche are still underspecified. In particular, all social interactions are not beneficial and individuals constantly face a trade-off between maximizing the number of cooperative interactions and minimizing exploitation risk. Therefore, motivation for social bonding should not operate indiscriminately but rather shape approach-avoidance decisions to maximize the number of successful interactions. According to this hypothesis then, social motivation should enhance responsiveness to cues that are relevant to assess the success of cooperative interactions. Highly socially motivated individuals should thus grant more importance to cooperation-related signals – such as trustworthiness, than to power-related cues – such as dominance.
In the present paper, we tested this hypothesis by investigating the weight individuals grant to cooperation-related cues during social decision-making. More precisely, based on previous work showing that approach-avoidance decisions can be decomposed into cooperation and power evaluations17–20, we compared the weight granted to cooperation-related cues to that granted to power-related cues. Our analysis relied on face evaluations, a major determinant of social interactions21. Face evaluations indeed predict who participants trust in economic games, who will be elected in political elections and who juries are most likely to condemn to death sentences22–24. Importantly, studies on face evaluations have shown that the weight granted to cooperation- and power-related cues, i.e. trustworthiness and dominance cues, varies across social contexts, which suggests that people adjust their social decisions flexibly according to the relevance of these cues. For instance, leader preferences are more driven by dominance in war-time, when physical strength is important, than in peace-time25,26. Going one step further, we hypothesized that this flexibility also operates across individuals and that motivation for social bonding is associated with an increase in the importance granted to trustworthiness to produce social decisions.
To test the hypothesis that the motivation to form social bonds is associated with a higher weight granted to cooperation-related cues, we first examined participants’ reliance on cooperation- and power-related cues to produce judgments of threat, which are key to produce avoidance decisions. More precisely, we asked 60 participants to rate 40 faces on threat, trustworthiness and dominance (Figure 1A). We reconstructed their two-dimensional threat space, by modelling threat evaluations as a function of perceived dominance and perceived trustworthiness. Following the analysis plan used in Todorov et al.’s paper27, our model of threat evaluations included linear, quadratic and interaction effects of perceived trustworthiness and perceived dominance.

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Results

As can be seen in Figure 1B, faces perceived as less trustworthy and more dominant were rated as more threatening (bT = -0.35 ± 0.05, t(2316) = – 15.25, p < .001; bD = 0.35 ± 0.04, t(2316) = 17.32, p < .001; Figure 1B). In addition, a quadratic effect of dominance indicated that threat evaluations were more sensitive to higher than to lower levels of dominance (bD^2 = 0.21 ± 0.07, t(2316) = 6.18, p < .001 = .024).
In line with our hypothesis, highly socially motivated participants granted more importance to perceived trustworthiness, but only to evaluate faces perceived as dominant (bT*D*SocMot = -0.17 ± 0.11, t(2316) = -2.97, p = .042; no other significant effect of social motivation was found: all ps > .119; Figure 1B). This result thus confirms and refines the hypothesized effect of the motivation for social bonding on approach-avoidance behaviour by revealing that the association between higher levels of social motivation and a higher weight granted to cooperation-related cues might be specific to the evaluation of powerful individuals.
We tested the robustness of this finding in two ways28. Firstly, by replicating the same experiment on 30 participants tested in the lab using avatar faces varying in dominance and trustworthiness, and then by extending this result to the opposite end of the approach-avoidance continuum through the investigation of likeability evaluations (60 participants).
As expected, the association between the motivation to form social bonds and an increased weight granted to trustworthiness to evaluate dominant faces was confirmed in the experiment on threat evaluation conducted in lab (bT*D*SocMot = -0.31 ± 0.14, t(2359) = -4.26, p = .006). The reconstruction of the two-dimensional likeability space replicated the general approach-avoidance pattern found in the threat evaluation studies, with more trustworthy and less dominant faces perceived as more likeable (bT = 0.38 ± 0.03, t(2317) = 21.87, p < .001 ; bD = -0.34 ± 0.03, t(2317) = -22.22, p < .001) and likeability ratings being more sensitive to higher than to lower levels of dominance (bD^2 = -0.15 ± 0.08, t(2317) = -5.40, p < .001; Figure 1C). Even more importantly, the effect of the motivation for social bonding on the combination of perceived trustworthiness and perceived dominance was also evidenced in likeability evaluations (bT*D*SocMot = 0.19 ± 0.09, t(2317) = 3.93, p < .001; Figure 1C). Finally, a meta-analysis conducted on all three social evaluation experiments further confirmed the association between high levels of social motivation and a higher weight granted to trustworthiness for the evaluation of dominant faces (bT*D*SocMot = -0.21 ± 0.07, z = 6.33, p < .001).

Table of contents :

CHAPTER ONE. FACE EVALUATIONS AS AN ENTRY POINT INTO SOCIAL COGNITION 
Importance of face evaluations
Functional bases of face evaluations
One face, multiple evaluations
CHAPTER TWO. INVESTIGATION OF AN INTERNAL VARIABLE: STUDY OF SOCIAL MOTIVATION 
Social motivation as cooperative strategy
Paper 1: Motivation for social bonding promotes high-stakes cooperative strategies, Safra, L., Wyart, V., Baumard, N., Chevallier, C.
Effect of social motivation across populations
Paper 2: Distinct effects of social motivation on face evaluations in adolescents with and without autism, Safra, L., Ioannou, C., Amsellem, F., Delorme, R., Chevallier, C.
Social motivation as a high-stake cooperative strategy
Towards new investigations of cooperative strategies
CHAPTER THREE. INVESTIGATION OF THE COGNITIVE PROCESSES UNDERLYING SOCIAL CHOICES: STUDY OF LEADER CHOICES 
An ecological approach to human behavior
Childhood environment and social preferences
Paper 3: Childhood harshness predicts long-lasting leader preferences Safra, L., Algan, Y., Tecu, T., Grèzes, J., Baumard, N., Chevallier, C.
An evolutionary perspective on leader preferences
Paper 4: Why would anyone elect a narcissistic untrustworthy leader? Safra, L., Baumard, N., Chevallier, C.
Political attitudes as behavioral responses to the environment
CHAPTER FOUR. GENERAL DISCUSSION 
An original approach to study social behavior
Beyond faces and social interactions
From the observer to the target
Limitations of the cooperation-power model
EPILOGUE. FACE EVALUATIONS, AN EVOLUTIONARY PUZZLE 
An evolutionary perspective on face evaluations
Puzzle 1. Face evaluations accuracy
Puzzle 2. Signaling untrustworthiness
GENERAL REFERENCES 
APPENDIX

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