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Social economic decision-making considers the well-being and emotions of others. Unlike traditional economics which routinely assumes that individuals care only about their own outcomes, behavioral economics and neuroeconomics offer research strategies which help us explore our social motivations. This dissertation consists of three essays studying the underlying behavioral and neural mechanisms of individuals' social economic decision-making. The analyses focus on investigating experimentally how humans make decisions in three distinct social economic environments. Chapter 2 examines how individuals react to hold-up when explicit promises are available. Hold-up happens when two parties can form an incomplete contract to cooperate, but the agreement may fall apart due to concerns about the other party gaining bargaining power. We propose that a belief-dependent frustration anger model can explain behavior about investment, cooperation, and costly punishment in a hold-up environment. We show experimentally that communication improves cooperation and increases efficiency. Promises lead to cooperation, and broken promises lead to costly punishment. Chapter 3 explores threats' deterrence effect and credibility in an ultimatum bargaining environment where two parties can both benefit over trade but have a conflict of interests. We show that a belief-dependent frustration anger model captures the relationship among messages, beliefs, and behavior. Our design permits the observation of communicated threats, credibility, and deterrence. As we hypothesize, messages convey intention to punish the opponents (threats) changes players' expectations, that first movers are largely deterred by the threats and second movers' threats are credible. Threats lead to deterrence and greater propensity for costly punishment. Chapter 4 investigates the neural basis of individuals' charity donation behavior in a modified dictator game. The right temporoparietal junction (rTPJ) has been associated with social decision-making, but the exact neural mechanism of charitable giving remains unknown. In our experiment, participants allocate money between themselves and a charity in a graphical revealed preference task, that measures both parameterized other-regarding preferences and economic rationality (Monotonicity, WARP, and GARP). We find evidence for a causal role of the rTPJ in determining fairness preferences and economic rationality. / Doctor of Philosophy / Social economic decision-making considers the well-being and emotions of others. Individuals engage in social economic decision-making on a daily basis, for example, negotiating over an offer, investing or cooperating on a project, bargaining over a purchase, or interacting with friends or strangers. Each of these decisions involves a variety of motivations including money for oneself, the well-being of others, each participants’ emotions and future relationships. Because of the complex nature of social economic decisions we need to employ an interdisciplinary research strategy. Behavioral economics applies psychological insights to economic problems and allows us to model the behavior of people who care about more than just money. Neuroeconomics integrates neuroscientific techniques and information about how the brain works to further expand our set of research tools. In this dissertation, we use all of these methods to explore how people make economic decisions in three distinct social scenarios. All three scenarios are especially intriguing since they represent different ways in which individuals integrate “others” into their own decision-making process. First, hold-up happens when two parties can form an incomplete agreement to cooperate and achieve higher efficiency together, however, the agreement may fall apart due to concerns about the other party gaining more bargaining power. In a historic example, Fisher Body had an exclusive supply agreement with General Motors. When the demand for cars increased sharply, Fisher Body held up General Motors by increasing prices. Second, negotiation is a situation where two parties can both benefit from trade, but they have conflicting interests. Third, individuals who engage in charity donations often sacrifice themselves monetarily to improve well-being of others. The scientific mission of this dissertation is to advance understanding of how individuals engage in social decision-making. In particular, we examine how communication (promises and threats) influences decision-making involving hold-up and negotiation respectively, and explore the neural mechanism governing altruism and charitable giving. We find evidence that communication enhances cooperation and efficiency in social economic decision-making through by changing expectations about monetary payoffs. In addition, we find evidence that the neural circuits responsible for fair-minded behavior also play a role in regulating economic rationality. This dissertation improves our understanding about how humans engage in social exchanges on both behavioral and neural levels.

Impaired social functioning conferred by mental illnesses has been constantly implicated in previous literatures. However, studies of social abnormalities in psychiatric conditions are often challenged by the difficulties of formalizing dynamic social exchanges and quantifying their neurocognitive underpinnings. Recently, the rapid growth of computational psychiatry as a new field along with the development of multiplayer economic paradigms provide powerful tools to parameterize complex interpersonal processes and identify quantitative indicators of social impairments. By utilizing these methodologies, the current set of studies aimed to examine social decision making during multiplayer economic games in participants diagnosed with depression (study 1) and combat-related post-traumatic stress disorder (PTSD, study 2), as well as an online population with elevated symptoms of borderline personality disorder (BPD, study 3). We then quantified and disentangled the impacts of multiple latent decision-making components, mainly social valuation and social learning, on maladaptive social behavior via explanatory modeling. Different underlying alterations were revealed across diagnoses. Atypical social exchange in depression and BPD were found attributed to altered social valuation and social learning respectively, whereas both social valuation and social learning contributed to interpersonal dysfunction in PTSD. Additionally, model-derived indices of social abnormalities positively correlated with levels of symptom severity (study 1 and 2) and exhibited a longitudinal association with symptom change (study 1). Our findings provided mechanistic insights into interpersonal difficulties in psychiatric illnesses, and highlighted the importance of a computational understanding of social function which holds potential clinical implications in differential diagnosis and precise treatment. / Doctor of Philosophy / People with psychiatric conditions often suffer from impaired social relationships due to an inability to engage in everyday social interactions. As different illnesses can sometimes produce the same symptoms, social impairment can also have different causes. For example, individuals who constantly avoid social activities may find them less interesting or attempt to avoid potential negative experiences. While those who display elevated aggression may have a strong desire for social dominance or falsely believe that others are also aggressive. However, it is hard to infer what drives these alterations by just observing the behavior. To address this question, we enrolled people with three different kinds of psychopathology to play an interactive game together with another player and mathematically modeled their latent decision-making processes. By comparing their model parameters to those of the control population, we were able to infer how people with psychopathology made the decisions and which part of the decision-making processes went wrong that led to disrupted social interactions. We found altered model parameters differed among people with major depression, post-traumatic stress disorder and borderline personality disorder, suggesting different causes underlying impaired social behavior observed in the game, the extent of which also positively correlated with their psychiatric symptom severity. Understanding the reasons behind social dysfunctions associated with psychiatric illnesses can help us better differentiate people with different diagnoses and design more effective treatments to restore interpersonal relationships.

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Esta dissertação visa abordar e dar início a um diálogo sobre a tomada de decisão social juntando aspectos de Administração de Empresas, Psicologia e Neurofisiologia. Primeiramente uma abordagem da evolução do pensamento sobre tomada de decisão é repassada com os conceitos de Simon (1955, 1959, 1979) na sua discussão sobre racionalidade completa e limitada. Isso se dá quando se nota que o ser humano possui limitações na sua racionalidade. Também, nota-se que o nível de incerteza e a complexidade inerente dos problemas aumentou. Soma-se a isso o fato de que, segundo Franks (2010) cada vez mais os seres humanos dependem da interação social para viver. Esse fato torna importante a consideração de aspectos emocionais, de memória e de comportamento. Aspectos de importância da Psicologia que são tratados junto com outros como emoção, cognição e percepção com os trabalhos de Elster (1998), Pretz, Naples e Sternberg (2003). Aspectos de consciência, vieses e heurísticas trazidos por Damásio (1996, 2011), Bazerman e Moore (2010) e Kahneman (2011) auxiliam na compreensão do fenômeno psicológico nessas interações e como eles impactam o processo decisório. Contudo, como melhor compreender a cognição? De onde surgem os comportamentos? Os conceitos de Neurofisiologia podem auxiliar. De forma a iniciar a integração de aspectos da Neurofisiologia na tomada de decisão utilizou-se Bear, Connors e Paradiso (2008), Ohme et al. (2009), entre outros. Foi criado um modelo, baseado na revisão da literatura realizada, visando determinar onde a decisão social poderia ocorrer e como ela poderia se dar em um ambiente organizacional. Dois grupos em uma empresa de pequeno porte foram observados. Ambos os grupos tinham quatro integrantes. No Grupo A três reuniões foram acompanhadas, no Grupo B duas reuniões foram acompanhadas. Utilizaram-se câmeras filmadoras para gravar os encontros de modo que isso permitisse a posterior análise das interações e linguagens verbal e não verbal do grupo. De modo a identificar os aspectos psicológicos dos grupos cinco testes foram aplicados: Wisconsin Card Sorting Game, Iowa Gambling Task, G- 36, Atenção Concentrada e Mini-Plus. Por fim, a revisão de literatura sobre aspectos Neurofisiológicos deu luz a possíveis ligações entre os resultados e esses conceitos. Os principais resultados demonstram que foi possível identificar uma ligação entre as três ciências no que toca a tomada de decisão nas organizações analisadas, tendo-se verificado que essas decisões ocorrem em dois passos principais: o individual e o social. / This master´s thesis aims to approach and start a dialogue about social decision making linking aspects coming from Business Administration, Psychology and Neurophysiology. First an approach regarding the evolution on the thought about decision making is given with the help of concepts from Simon (1959, 1955 e 1979) with his discussion about complete and limited rationality. This discussion start when the human being acknowledges the limitations of his own rationality. Also it is easy to notice the expanding levels of the inherent complexity and uncertainty within the decision making process. Adding to that the fact that, according to Franks (2010), humans have never been more dependent on social interaction in order to live. This facts bring out the importance in considering aspects such as emotions, memory and behavior. This is where Psychology plays its cards and such concepts as emotion, cognition and perception with the help of the works of Elster (1998), Pretz, Naples e Sternberg (2003) are presented. Together in the quest of explaining the psychological phenomenon and how it affects the decision making process aspects of conscience, biases and heuristics brought by Damásio (1996 e 2011), Bazerman e Moore (2010) e Kahneman (2011) are considered. However, how to better comprehend cognition? Where do behaviors come from? Neurophysiology can play an important role in to help answer these questions. As a way to start this link between these concepts and the decision making literature, Bear, Connors e Paradiso (2008), Ohme et al. (2009), among others, were used. A model was developed, based on the revised literature trying to identify where and how the decision making process is present in a social environment. Two groups from a small company were studied. Both groups had four participants. Group A had three meetings accompanied and Group B had two meetings accompanied. Video cameras were uses to tape the meetings in order to allow the analyses of the group´s interactions and verbal and non-verbal language. To help identify the group´s psychological traits, five tests were applied individually: Wisconsin Card Sorting Game, Iowa Gambling Task, G-36, Concentrated Attention and Mini-Plus. Finally a revision of the literature on Neurophysiology sheds light on possible connections between the results and such concepts. The main results show that it is possible to link the three sciences regarding the decision making process in the organizations analyzed, it is concluded that the decision occur in two main steps: individual and social.

Esta dissertação visa abordar e dar início a um diálogo sobre a tomada de decisão social juntando aspectos de Administração de Empresas, Psicologia e Neurofisiologia. Primeiramente uma abordagem da evolução do pensamento sobre tomada de decisão é repassada com os conceitos de Simon (1955, 1959, 1979) na sua discussão sobre racionalidade completa e limitada. Isso se dá quando se nota que o ser humano possui limitações na sua racionalidade. Também, nota-se que o nível de incerteza e a complexidade inerente dos problemas aumentou. Soma-se a isso o fato de que, segundo Franks (2010) cada vez mais os seres humanos dependem da interação social para viver. Esse fato torna importante a consideração de aspectos emocionais, de memória e de comportamento. Aspectos de importância da Psicologia que são tratados junto com outros como emoção, cognição e percepção com os trabalhos de Elster (1998), Pretz, Naples e Sternberg (2003). Aspectos de consciência, vieses e heurísticas trazidos por Damásio (1996, 2011), Bazerman e Moore (2010) e Kahneman (2011) auxiliam na compreensão do fenômeno psicológico nessas interações e como eles impactam o processo decisório. Contudo, como melhor compreender a cognição? De onde surgem os comportamentos? Os conceitos de Neurofisiologia podem auxiliar. De forma a iniciar a integração de aspectos da Neurofisiologia na tomada de decisão utilizou-se Bear, Connors e Paradiso (2008), Ohme et al. (2009), entre outros. Foi criado um modelo, baseado na revisão da literatura realizada, visando determinar onde a decisão social poderia ocorrer e como ela poderia se dar em um ambiente organizacional. Dois grupos em uma empresa de pequeno porte foram observados. Ambos os grupos tinham quatro integrantes. No Grupo A três reuniões foram acompanhadas, no Grupo B duas reuniões foram acompanhadas. Utilizaram-se câmeras filmadoras para gravar os encontros de modo que isso permitisse a posterior análise das interações e linguagens verbal e não verbal do grupo. De modo a identificar os aspectos psicológicos dos grupos cinco testes foram aplicados: Wisconsin Card Sorting Game, Iowa Gambling Task, G- 36, Atenção Concentrada e Mini-Plus. Por fim, a revisão de literatura sobre aspectos Neurofisiológicos deu luz a possíveis ligações entre os resultados e esses conceitos. Os principais resultados demonstram que foi possível identificar uma ligação entre as três ciências no que toca a tomada de decisão nas organizações analisadas, tendo-se verificado que essas decisões ocorrem em dois passos principais: o individual e o social. / This master´s thesis aims to approach and start a dialogue about social decision making linking aspects coming from Business Administration, Psychology and Neurophysiology. First an approach regarding the evolution on the thought about decision making is given with the help of concepts from Simon (1959, 1955 e 1979) with his discussion about complete and limited rationality. This discussion start when the human being acknowledges the limitations of his own rationality. Also it is easy to notice the expanding levels of the inherent complexity and uncertainty within the decision making process. Adding to that the fact that, according to Franks (2010), humans have never been more dependent on social interaction in order to live. This facts bring out the importance in considering aspects such as emotions, memory and behavior. This is where Psychology plays its cards and such concepts as emotion, cognition and perception with the help of the works of Elster (1998), Pretz, Naples e Sternberg (2003) are presented. Together in the quest of explaining the psychological phenomenon and how it affects the decision making process aspects of conscience, biases and heuristics brought by Damásio (1996 e 2011), Bazerman e Moore (2010) e Kahneman (2011) are considered. However, how to better comprehend cognition? Where do behaviors come from? Neurophysiology can play an important role in to help answer these questions. As a way to start this link between these concepts and the decision making literature, Bear, Connors e Paradiso (2008), Ohme et al. (2009), among others, were used. A model was developed, based on the revised literature trying to identify where and how the decision making process is present in a social environment. Two groups from a small company were studied. Both groups had four participants. Group A had three meetings accompanied and Group B had two meetings accompanied. Video cameras were uses to tape the meetings in order to allow the analyses of the group´s interactions and verbal and non-verbal language. To help identify the group´s psychological traits, five tests were applied individually: Wisconsin Card Sorting Game, Iowa Gambling Task, G-36, Concentrated Attention and Mini-Plus. Finally a revision of the literature on Neurophysiology sheds light on possible connections between the results and such concepts. The main results show that it is possible to link the three sciences regarding the decision making process in the organizations analyzed, it is concluded that the decision occur in two main steps: individual and social.

Esta dissertação visa abordar e dar início a um diálogo sobre a tomada de decisão social juntando aspectos de Administração de Empresas, Psicologia e Neurofisiologia. Primeiramente uma abordagem da evolução do pensamento sobre tomada de decisão é repassada com os conceitos de Simon (1955, 1959, 1979) na sua discussão sobre racionalidade completa e limitada. Isso se dá quando se nota que o ser humano possui limitações na sua racionalidade. Também, nota-se que o nível de incerteza e a complexidade inerente dos problemas aumentou. Soma-se a isso o fato de que, segundo Franks (2010) cada vez mais os seres humanos dependem da interação social para viver. Esse fato torna importante a consideração de aspectos emocionais, de memória e de comportamento. Aspectos de importância da Psicologia que são tratados junto com outros como emoção, cognição e percepção com os trabalhos de Elster (1998), Pretz, Naples e Sternberg (2003). Aspectos de consciência, vieses e heurísticas trazidos por Damásio (1996, 2011), Bazerman e Moore (2010) e Kahneman (2011) auxiliam na compreensão do fenômeno psicológico nessas interações e como eles impactam o processo decisório. Contudo, como melhor compreender a cognição? De onde surgem os comportamentos? Os conceitos de Neurofisiologia podem auxiliar. De forma a iniciar a integração de aspectos da Neurofisiologia na tomada de decisão utilizou-se Bear, Connors e Paradiso (2008), Ohme et al. (2009), entre outros. Foi criado um modelo, baseado na revisão da literatura realizada, visando determinar onde a decisão social poderia ocorrer e como ela poderia se dar em um ambiente organizacional. Dois grupos em uma empresa de pequeno porte foram observados. Ambos os grupos tinham quatro integrantes. No Grupo A três reuniões foram acompanhadas, no Grupo B duas reuniões foram acompanhadas. Utilizaram-se câmeras filmadoras para gravar os encontros de modo que isso permitisse a posterior análise das interações e linguagens verbal e não verbal do grupo. De modo a identificar os aspectos psicológicos dos grupos cinco testes foram aplicados: Wisconsin Card Sorting Game, Iowa Gambling Task, G- 36, Atenção Concentrada e Mini-Plus. Por fim, a revisão de literatura sobre aspectos Neurofisiológicos deu luz a possíveis ligações entre os resultados e esses conceitos. Os principais resultados demonstram que foi possível identificar uma ligação entre as três ciências no que toca a tomada de decisão nas organizações analisadas, tendo-se verificado que essas decisões ocorrem em dois passos principais: o individual e o social. / This master´s thesis aims to approach and start a dialogue about social decision making linking aspects coming from Business Administration, Psychology and Neurophysiology. First an approach regarding the evolution on the thought about decision making is given with the help of concepts from Simon (1959, 1955 e 1979) with his discussion about complete and limited rationality. This discussion start when the human being acknowledges the limitations of his own rationality. Also it is easy to notice the expanding levels of the inherent complexity and uncertainty within the decision making process. Adding to that the fact that, according to Franks (2010), humans have never been more dependent on social interaction in order to live. This facts bring out the importance in considering aspects such as emotions, memory and behavior. This is where Psychology plays its cards and such concepts as emotion, cognition and perception with the help of the works of Elster (1998), Pretz, Naples e Sternberg (2003) are presented. Together in the quest of explaining the psychological phenomenon and how it affects the decision making process aspects of conscience, biases and heuristics brought by Damásio (1996 e 2011), Bazerman e Moore (2010) e Kahneman (2011) are considered. However, how to better comprehend cognition? Where do behaviors come from? Neurophysiology can play an important role in to help answer these questions. As a way to start this link between these concepts and the decision making literature, Bear, Connors e Paradiso (2008), Ohme et al. (2009), among others, were used. A model was developed, based on the revised literature trying to identify where and how the decision making process is present in a social environment. Two groups from a small company were studied. Both groups had four participants. Group A had three meetings accompanied and Group B had two meetings accompanied. Video cameras were uses to tape the meetings in order to allow the analyses of the group´s interactions and verbal and non-verbal language. To help identify the group´s psychological traits, five tests were applied individually: Wisconsin Card Sorting Game, Iowa Gambling Task, G-36, Concentrated Attention and Mini-Plus. Finally a revision of the literature on Neurophysiology sheds light on possible connections between the results and such concepts. The main results show that it is possible to link the three sciences regarding the decision making process in the organizations analyzed, it is concluded that the decision occur in two main steps: individual and social.

Les évaluations faciales sont un élément central des comportements sociaux, influençant un large spectre de décisions, allant du choix du romantique au choix politique, mais sont également le sujet de grandes variations individuelles. Dans cette thèse, je propose que l'analyse des différences individuelles dans l'utilisation de différents signaux sociaux, notamment ceux de coopération et de pouvoir, lors des évaluations faciales est un outil prometteur pour l'étude des comportements sociaux ; j'applique cette approche de deux façons. Dans un premier temps, pour examiner l'hypothèse selon laquelle la motivation sociale correspond à une adaptation aux environnements coopératifs. À travers six études, je montre que la motivation sociale est associée à une plus grande importance donnée aux signaux de coopération, confirmant ainsi une prédiction centrale de cette théorie. Dans un second temps, j'étudie les mécanismes cognitifs impliqués dans les choix politiques, en examinant leurs réponses à différents signaux de l'environnement. Dans un premier travail expérimental, je montre que l'expérience précoce de la précarité est associée à une préférence pour les hommes forts. À partir de ces résultats, je développe une théorie originale sur les préférences politiques selon laquelle les choix politiques sont orientés vers les individus perçus comme les plus aptes à réussir en tant qu'individus et non en tant que chefs de groupe. En résumé, tout au long de cette thèse, je présente un nouveau cadre de travail pour l'étude des décisions sociales et je montre comment il permet éclairer les mécanismes cognitifs sous-tendant les comportements sociaux ainsi que leurs bases évolutives. / Face evaluations are a crucial component of social behavior, influencing a large range of social decisions from mating to political vote. Face evaluations are also susceptible to substantial individual differences. In this thesis, I propose that individual differences in face evaluations constitute a promising tool to investigate social behavior through the analysis of variations in the weight granted to different social signals, and notably cooperation- and power-related cues. I apply this approach in two ways. First, I examine the hypothesis that social motivation can be construed as an adaptation to highly cooperative environments. Across six studies, I confirm a central prediction of this theory, by revealing that highly socially motivated individuals grant a higher importance to cooperation-related signals. Second, I investigate the cognitive mechanisms underlying political choices by examining their responses to different environmental signals. In a study on leader preferences in children and in adults, I show that early exposure to environmental harshness is associated with a preference for stronger leaders. Building on these results, I then develop an original theory on political choices stating that leader preferences are biased towards the candidates perceived as the most competent for succeeding in the current context, independently of their leadership abilities. To summarize, my thesis puts forward a new framework to investigate social decisions based on individual variations in face evaluations and sheds light on the cognitive processes underlying social behavior as well as their evolutionary bases.

No description available.

Les comportements sociaux coopératifs sont longtemps restés un obstacle aux modèles de choix rationnel, obstacle qu'incarnent des dilemmes sociaux où un individu suivant son intérêt personnel est incité à exploiter la coopération d'autrui à son seul avantage. Je détaillerai tout d'abord comment la coopération peut apparaître un choix sensé lorsque elle est envisagée dans un contexte naturel et réel. Un regard à travers l'anthropologie, la psychologie et la neurobiologie conduit à appréhender la coopération davantage comme une adaptation et un apprentissage que comme un défaut de rationalité. Les émotions jouent un rôle essentiel dans ces processus, et je présenterai en quoi les exprimer aide les êtres humains à se synchroniser et à coopérer. Le sourire est souvent invoqué comme exemple d'un signal universel de coopération et d'approbation, une propriété intimement liée à son expression répétée lors de tâches collaboratives. Malgré tout, on en sait encore peu sur la manière précise dont le sourire et les autres expressions interviennent dans la prise de décision sociale, et en particulier sur le traitement des situations d'incongruence où un sourire accompagnerait une défection. Ce point est le cœur de l'étude expérimentale que je rapporte dans ce manuscrit. J'ai réalisé deux expériences confrontant les participants à un dilemme social dans lequel ils pouvaient investir une somme d'argent auprès de différents joueurs informatisés susceptibles de se l'accaparer, ou, au contraire, de la rétribuer avec intérêts. Les joueurs virtuels étaient personnalisés par un visage dont l'expression pouvait changer après le choix du participant: certains affichaient ainsi des émotions incongruentes avec leur ``décision'' subséquente de rétribuer ou non l'investissement du sujet. Malgré les différences méthodologiques, ces deux expériences ont montré que les expressions incongruentes altéraient la capacité des participants à jauger la propension des joueurs virtuels à rétribuer leurs investissements après une ou plusieurs interactions. Cet effet s'est manifesté tant au travers de rapports explicites que dans les investissements effectués. Dans leurs détails, les résultats de ces expériences ouvrent de nombreuses perspectives expérimentales, et appellent à la construction d'un modèle unifié de la décision sociale face-à-face qui intégrerait les nombreuses connaissances apportées ces dernières années par l'étude des grandes fonctions cognitives, tant au niveau expérimental, théorique que neurobiologique. / For few decades, rational choice theories failed to properly account for cooperative behaviors. This was illustrated by social dilemmas, games where a self-motivated individual will be tempted to exploit others' cooperative behavior, harming them for his own personal profit. I will first detail how cooperation may rise as a reasonable --- if not rational --- behavior, provided that we consider social interactions in a more realistic context that rational choice theories initially did. From anthropology to neurobiology, cooperation is understood as an efficient adaptation to this natural environment rather than a quirky, self-defeating behavior. Because pertinent information is often lacking or overwhelming, too complex or ambiguous to deal with, it is essential to communicate, to share, and to trust others. Emotions, and their expression, are a cornerstone of humans' natural and effortless navigation in their social environment. Smiles for instance are universally known as a signal of satisfaction, approbation and cooperation. Like other emotional expressions, they are automatically and preferentially treated. They elicit trust and cooperative behaviors in observers, and are ubiquitous in successful collaborative interactions. Beside that however, few is known about how others' expressions are integrated into decision making. That was the focus of the experimental study I relate in this manuscript. More specifically, I investigated how decisions in a trust-based social dilemma are influenced by smiles which are either displayed along a cooperative or defective behavior (``congruently'' and ``incongruently'', resp.). I carried out two experiments where participants played an investment game with different computerized virtual partners playing the role of trustees. Virtual trustees, which were personalised with a facial avatar, could either take and keep participants investment, or reciprocate it with interests. Moreover, they also displayed facial reactions, that were either congruent or incongruent with their computerized ``decision'' to reciprocate or not. Even if the two experiments presented some methodological differences, they were coherent in that they both showed that participants were altered in remembering a virtual trustee's behavior if the latter expressed incongruent emotions. This was observed from participants' investments in game, and from their post-experimental explicit reports. If many improvements to my experimental approach remain to be done, I think it already completes the existing literature with original results. Many interesting perspectives are left open, which appeal for a deeper investigation of face-to-face decision making. I think it constitutes a theoretical and practical necessity, for which researchers will be required to unify the wide knowledge of the major cognitive functions which was gathered over the last decades.