Kameda, T.（亀田達也）, Inukai, K.（犬飼佳吾）, Higuchi, S., Ogawa, A., Kim, H., Matsuda, T., & Sakagami, M. (2016). Rawlsian maximin rule operates as a common cognitive anchor in distributive justice and risky decisions. ロールズのマキシミン基準は分配的正義とリスキーな決定に際する一般的な認知的アンカーとして機能する Proceedings of the National Academy of Sciences, Published online before print September 29, 2016. doi: 10.1073/pnas.1602641113
Distributive justice concerns the moral principles by which we seek to allocate resources fairly among diverse members of a society. Although the concept of fair allocation is one of the fundamental building blocks for societies, there is no clear consensus on how to achieve “socially just” allocations. Here, we examine neurocognitive commonalities of distributive judgments and risky decisions. We explore the hypothesis that people’s allocation decisions for others are closely related to economic decisions for oneself at behavioral, cognitive, and neural levels, via a concern about the minimum, worst-off position. In a series of experiments using attention-monitoring and brain-imaging techniques, we investigated this “maximin” concern (maximizing the minimum possible payoff) via responses in two seemingly disparate tasks: third-party distribution of rewards for others, and choosing gambles for self. The experiments revealed three robust results: (i) participants’ distributive choices closely matched their risk preferences—“Rawlsians,” who maximized the worst-off position in distributions for others, avoided riskier gambles for themselves, whereas “utilitarians,” who favored the largest-total distributions, preferred riskier but more profitable gambles; (ii) across such individual choice preferences, however, participants generally showed the greatest spontaneous attention to information about the worst possible outcomes in both tasks; and (iii) this robust concern about the minimum outcomes was correlated with activation of the right temporoparietal junction (RTPJ), the region associated with perspective taking. The results provide convergent evidence that social distribution for others is psychologically linked to risky decision making for self, drawing on common cognitive–neural processes with spontaneous perspective taking of the worst-off position.