Published papers

Prejudice related to the coronavirus disease 2019 (COVID-19) is a social issue worldwide. A possible psychological factor that promotes prejudice is the belief in just deserts (BJD) regarding individuals infected with COVID-19 (i.e., the belief that the infected individual deserves to be infected). The BJD is based on the belief in immanent justice. It is reportedly higher in Japan than in other countries. Therefore, we conducted a cross-sectional study to investigate the BJD among Japanese individuals and clarify its associations with demographic factors or infection-related and socio-psychological characteristics. To this end, we conducted an online questionnaire survey in Japan from August 7–8, 2020, with 1,207 respondents aged 20–69 years. We performed screening to exclude inappropriate responses. We investigated the association between the BJD and demographic factors such as gender and age. We also investigated the association between the BJD and infection-related and socio-psychological characteristics, including risk perception of COVID-19 infection and human rights restrictions (i.e., the degree of agreement with government restrictions on individuals’ behavior during emergencies). Among the surveyed items, human rights restrictions showed a strong association with BJD, followed by risk perception of COVID-19 infection. Men had a slightly higher BJD than women. Our study is significant in that it is the first to investigate the items associated with the BJD, thereby providing foundational information for revising individual perceptions of justice related to COVID-19 and solving prejudice-related issues.

Discrimination, which arose during the coronavirus disease 2019 outbreak, is a global public health issue. This study aimed to provide fundamental knowledge in proposing control measures to mitigate discrimination. We focused on two psychological variables: belief in just deserts (BJD, i.e., the belief that the infected individual deserves to be infected), a psychological factor that potentially promotes discrimination and prejudice, and human rights restrictions (HRR; i.e., the degree of individuals’ agreement with government restrictions on citizens’ behavior during emergencies). Differences in these items, as well as their annual trends from 2020 to 2022, were examined in Japan, the United States (US), the United Kingdom (UK), Italy, and China. In addition, the associations between BJD and HRR by country and year and the direction of the associations between them in Japan and Italy were analyzed. Online surveys were conducted annually, with 392–518 participants per country and year. The BJD was higher in Japan and lower in the UK. BJD increased significantly from 2020 to 2021 in all countries, except in China. Meanwhile, HRR was higher in China and lower in Japan. The HRR decreased from 2020 to 2021 in Japan and decreased from 2020 to 2022 in the US, the UK, and Italy. There were significant positive associations between BJD and HRR in Japan and Italy. Cross-lagged panel models revealed positive bidirectional associations between BJD and HRR in Japan and Italy, respectively, indicating that the HRR declined among those with weak BJD and that the BJD increased among those with high HRR. In Japan and Italy, the dissemination of public messages targeting those with a high HRR in the early stages of an infectious disease outbreak could potentially mitigate the adverse impact of the BJD, eventually reducing discrimination, especially when the infection is not attributed to the fault of the infected individuals.

In this study, we investigated the cognitive processes and nonverbal cues used to detect altruism in three experiments based on a zero-acquaintance video presentation paradigm. Cognitive mechanisms of altruism detection are thought to have evolved in humans to prevent subtle cheating. Several studies have demonstrated that people can correctly estimate levels of altruism in others. In this study, we asked participants to distinguish altruists from non-altruists in video clips using the Faith game. Participants decided whether they could trust allocation of money to the targets who were videotaped while talking to the experimenter. In our first experiment, we asked the participants to play the Faith game under cognitive load. The accuracy of altruism detection was not reduced when participants simultaneously performed a cognitive task, suggesting that altruist detection is rapid and effortless. In the second experiment, we investigated the effects of affective status on the accuracy of altruism detection. Compared with participants in a positive mood, those in a negative mood were more hesitant to trust videotaped targets. However, the accuracy with which altruism levels were detected did not change when we manipulated participants’ moods. In the third experiment, we investigated the facial cues by which participants detected altruists. Participants could not detect altruists when the upper half of the target’s face was hidden, suggesting that judgment cues exist around the eyes. We also conducted a meta-analysis on the effect size in each experimental condition to verify the robustness of altruism detection ability.

In elucidating the spread of risk information through microblogging, it is important to understand the behaviors of numerous average users, in addition to the activities of authorities. We followed the transmission pathways of 10 actual widely spread tweets concerning several risk information topics, including natural disasters, nuclear disasters, and infectious diseases, and we identified the types of risk that affected retweeting by classifying each tweet based on Slovic's risk-perception model. Furthermore, we examined the types of users who did and did not retweet the information. Users with few connections in the form of followers (i.e., people who are following a user) or followees (people a user is following), or with a low ratio of mutual followers within their connections, had a tendency to retweet a large amount of risk information, regardless of the type of risk involved. On the other hand, users with a high ratio of mutual followers exhibited a greater tendency to retweet risk information when it was perceived as dreadful, though they did not retweet risk information much on the whole. These results suggest that there are two mechanisms by which risk information is spread within the Twitter network: information exchange and social sharing of personal reactions.

We conducted a systematic review of conference papers in social psychology at two large psychology conferences in Japan: the Japanese Psychological Association and the Japanese Society for Social Psychology. The conference papers were effectively not subjected to peer review; hence, they were suitable for testing if psychologists selectively reported statistically significant findings without pressure from journal editors and reviewers. We investigated the distributions of z-values converted from the p-values reported in the articles presented at the 2013 and 2018 conferences. The z-curve analyses suggest the existence of selective reporting by the authors in 2013. The expected discovery rate (EDR) was much lower than the observed discovery rate (ODR; 7% vs. 76%, respectively), and the 95% confidence interval (CI) did not include the ODR. However, this does not mean that the set of studies completely lacked evidential value. The expected replication rate (ERR) was 31%; this is significantly higher than 5%, which was expected under the null hypothesis of no effect. Changes were observed between 2013 and 2018. The ERR increased (31% to 44%), and the EDR almost doubled (7% to 13%). However, the estimation of the maximum false discovery rate (FDR; 68% in 2013 and 35% in 2018) suggested that a substantial proportion of the reported findings were false positives. Overall, while social psychologists in Japan engaged in selective reporting, this does not mean that the entire field was covered with false positives. In addition, slight signs of improvement were observed in how they reported their findings. Still, the evidential value of the target studies was weak, even in 2018, allowing for no optimism.

Men's altruism may have evolved, via female choice, as a signal of either their genetic quality or their willingness to allocate resources to offspring. The possibility that men display altruism to signal their genetic quality may be tested by examining women's preference for men's altruism across the stages of the menstrual cycle. Because women can maximize reproductive benefits by mating with men who have "good genes" on high-fertility versus low-fertility days, women should show a heightened preference for male altruism on high-fertility days compared to low-fertility days, and this heightened preference should be more apparent when women evaluate men for short-term sexual relationships than for long-term committed relationships. The possibility that men display altruism to signal their willingness to provision, as opposed to their genetic quality, may be tested by examining women's preference for men's altruism toward different recipients. More specifically, altruistic behavior toward family members may reflect a willingness to provide resources for kin and, hence, willingness to provision, whereas altruistic behavior toward strangers may function as an honest signal of genetic quality. In two samples of young women (Ns = 131 and 481), we found no differences between high- and low-fertility participants in preference for men's altruism, and women preferred men's altruism more in long-term than short-term relationships. The findings suggest that men's altruistic behavior functions as a signal of willingness to provide resources rather than genetic quality.

This study describes the development and evaluation of the Self-Report Altruism Scale Distinguished by the Recipient (SRAS-DR). The relationship between an actor and a recipient is important for evolutionary studies of altruistic behavior. However, the existing scale for Japanese undergraduates does not distinguish recipients of altruistic behaviors. We developed a new self-report altruism scale based on an evolutionary viewpoint. In Study 1, undergraduate students described their altruistic behaviors in daily life, which we classified according to the recipients (family members, friends or acquaintances and strangers). Then we chose 21 items (7 items for each recipient class) to construct the SRAS-DR by using exploratory factor analyses. In Study 2, we investigated validity and reliability of the scale. The scores were significantly correlated with other relevant scales as well as with behavioral indicators. Test-retest reliability was high. These results indicate that the SRAS-DR has acceptable reliability and validity, and can be used in evolutionary studies of human altruism.

Factors contributing to individual differences of empathy were examined using behavioral genetics methodology. Data related to individual levels of empathy and parental warmth received during childhood were collected from approximately 450 pairs of twins (ages 14-33). A bivariate model analysis clarified that shared family environmental factors did not contribute to the formation of empathy. No common shared environmental factors were detected between empathy and parental warmth, either. The positive correlation between the two variables was mediated principally by genetics. The result does not support socialization theory, which holds that warm parenting nurtures children's empathy. - However, the subsequent gene-environment interaction model analysis revealed that shared family environmental factors significantly affected the formation of empathy for those with high or very low parental warmth. The results imply that individuals with a strong or very weak attachment to their parents were more influenced by the shared family environment.

Possible effects of external and internal factors affecting prosociality in Japanese undergraduates were investigated. We employed social support as an external factor and helping norms, self-consciousness, other-consciousness, self-esteem, and religious attitude as internal factors. Prosociality toward friends/acquaintances was significantly positively correlated with social support from siblings, social support from friends/acquaintances, self-sacrifice norms, and private self-consciousness, whereas prosociality toward strangers was significantly positively correlated with social support from mothers, private self-consciousness, and self-esteem but negatively correlated with social support from siblings. The results support claims of an altruism niche that rest on the assumption that prosociality can be maintained only in an environment or a society in which altruistic acts are rewarded. Among the internal factors, private self-consciousness was the only factor found to correlate with both aspects of prosociality. Higher scores on private selfconsciousness were related to irrational altruism, making people less susceptible to the features of particular situations and, consequently, producing reputational benefits.