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Max Planck Institute for Human Development
When sharing a common goal, confident and competent members are often motivated to contribute to the group, boosting its decision performance. However, it is unclear whether this process remains effective when members can opt in or out of group decisions and prioritize individual interests. Our laboratory experiment and cognitive modeling showed that confidence, competence, and a preference for risk motivated participants’ opt-out decisions. Whereas the majority decisions by voters who remained in the group were inferior to individual decisions by loners who opted out in an easy task, this was reversed in a difficult task. Bootstrap-simulation analyses decomposed these outcomes into the effects of group size and bias in the distribution of the voters’ accuracy accruing from the opt-in/out mechanism, demonstrating how these effects interacted with task difficulty. Our results suggest that the majority rule still works to tackle challenging problems even when individual interests are emphasized over collective performance.
In the digital era, new socially shared realities and norms emerge rapidly, whether they are beneficial or harmful to our societies. Although these are emerging properties from dynamic interaction, most research has centered on static situations where isolated individuals face extant norms. We investigated how perceptual norms emerge endogenously as shared realities through interaction, using behavioral and fMRI experiments coupled with computational modeling. Social interactions fostered convergence of perceptual responses among people, not only overtly but also at the covert psychophysical level that generates overt responses. Reciprocity played a critical role in increasing the stability (reliability) of the psychophysical function within each individual, modulated by neural activity in the mentalizing network during interaction. These results imply that bilateral influence promotes mutual cognitive anchoring of individual views, producing shared generative models at the collective level that enable endogenous agreement on totally new targets–one of the key functions of social norms.
According to the halo effect, person perceptions are globally biased by specific traits or characteristics. Attractive people are attributed positive traits like prosociality, health, and dominance. However, due to a strong focus on facial stimuli it remains unclear whether this effect can also be found for bodies. Furthermore, most studies involved observers from individualistic cultures. This preregistered study explored the cross-cultural consistency of halo effects for men’s faces and bodies. Facial photos and 3D body scans of 165 German men were judged separately for attractiveness, prosociality, health, and dominance by 123 German and 100 Japanese observers. Results were mostly cross-culturally consistent and revealed strong attractiveness halo effects for faces and bodies, and a dominance halo effect for bodies, but not faces. Further predictions of the one ornament hypothesis were supported. This study provides new insights on halo effects as cross-culturally consistent cognitive biases in person perception for faces and bodies.
People often need to make risky decisions for others, especially in policymaking, where a single decision can affect the welfare of a number of people. Given that risky decisions can yield variable outcomes and that people often evaluate policies after knowing the outcomes, the same risky policy can be evaluated differently depending on its outcome. Nevertheless, very little is known about how people make third-party evaluations of risky policies. Because people are sensitive to inequality among others, we predicted that the same policy would be evaluated more negatively if it leads to inequality rather than other outcomes. To examine this, we conducted a scenario experiment on risky and sure policies and investigated whether people’s distributive preferences moderated policy evaluation. We show that participants rated the risky policy lower when it yielded unequal situations between the recipients. Interestingly, participants did not evaluate the risky policy higher than the sure policy even when the risky policy yielded more desirable outcomes. In addition, participants who preferred sure distributions as decision makers or recipients showed the inequality aversion, whereas participants who preferred risky distributions showed no such pattern. Our results suggest that policy evaluation may be susceptible to the risks and inequality of outcomes among recipients.
Trust is a vital element of any society. Previous studies using trust games have provided insight into understandings of trusting behavior. However, investors' behaviors can be confounded by their risk preferences in the game, and little is known about the relationship between stake size and beliefs of others' good intentions underlying trust. We thus used a variant of the trust game and conducted two experiments to examine how stake size affects investors' beliefs about receivers' trustworthiness, with model‐based analyses. We showed that, when holding all else equal, investors trusted more, but their expectations of reciprocation declined as stake size increased. However, actual receivers' reciprocation rates showed the opposite trend to investors' pessimistic beliefs. Furthermore, following previous studies in social psychology, we hypothesized that investors' social preferences (social value orientation) moderated the beliefs underlying trust, but they had no explanatory powers in investors' expectations of reciprocation. These results suggest that peoples' naive beliefs about stake size play a more important role in trust decisions than expected.
第19回東大院生・教職員によるミニレクチャプログラム（主催：東京大学大学総合教育研究センター / 東京大学附属図書館）