Historical bombings, urban community, and prosociality: Application of the First internet lab-in-the-field experiment

This study examines how the endurance or destruction of urban communities shapes contemporary social preferences by utilizing an innovative Internet lab-in-the-field experiment (I-LFE). Traditional lab-in-the-field experiments (LFE), which investigate spatially distributed treatments on social behavior, often face logistical and geographical limitations. Our I-LFE effectively overcomes these constraints by conducting experiments entirely online, allowing flexible real-time subject matching. We leverage World War II bombings in Tokyo and Osaka, cities with diverse cultural contexts, where uniform neighborhood organizations ( tonarigumi ), established nationwide, experienced varying degrees of disruption due to air raid damage, providing an exogenous shock. We tested hypotheses regarding how neighborhood destruction, length of residence, and in-group distinctions affect contemporary prosocial behaviors. Using detailed prewar and postwar aerial imagery, we identified neighborhoods with similar prewar characteristics but significantly different levels of bombing damage. Residents from these neighborhoods participated in online economic games at scheduled times. Our key findings reveal that (1) long-term residents in heavily bombed neighborhoods exhibit heightened altruism specifically toward local in-group members, supporting the theory that collective trauma fosters conditional altruism; and (2) recent residents in less affected areas also demonstrate enhanced prosociality toward their local communities, indicating selective migration toward regions with established social networks. By pioneering the I-LFE methodology, this study significantly advances behavioral research capabilities in urban contexts. Additionally, our results highlight the enduring effects of collective memory and selective migration in shaping community-level prosocial outcomes decades after conflict. The findings enrich the literature on historical persistence, illuminating the complex mechanisms influencing prosocial behavior among long- and short-term residents in developed urban settings, where such research remains sparse. • Introducing the first-ever Internet-based lab-in-the-field experiment (I-LFE). • I-LFE addresses both geographical and financial barriers in urban behavioral studies. • Online survey respondents from Tokyo and Osaka simultaneously played the UG and DG. • Collective memory and selective migration shape long-lasting prosocial outcomes.