Stage 1 registered report examining agency and outcome valence on inter-brain synchrony during dyadic moral judgments

Inter-brain synchrony (IBS) has emerged as a promising marker of neural processes supporting social interaction, cooperation, and moral evaluation. Previous hyperscanning research shows that IBS increases during tasks involving joint attention, cooperation, or shared intentionality. Nevertheless, little is known about how agency-the extent to which individuals can influence outcomes-and outcome valence interact to shape neural alignment between people. Real-world social contexts often involve asymmetries in control and responsibility, and these dynamics may critically influence how individuals coordinate and evaluate one another's decisions. The present registered report outlines two experiments designed to examine the relationship between agency and outcome valence and IBS. In the first experiment, agency (high vs. low) and outcome valence (reward vs. punishment) are jointly manipulated during moral adjudications of economic game offers. We predict that high-agency contexts, especially when linked to punishing unfairness, will enhance IBS by fostering shared responsibility and coordinated evaluation. In the second experiment, asymmetric agency roles (equal, unilateral, none) are introduced to examine whether unequal distributions of control reduce IBS. We also explore directional influences from higher- to lower-agency partners. By systematically manipulating both the degree of agency and the valence of social outcomes, this research aims to advance theoretical accounts of joint moral decision-making and hierarchical social interaction. The findings will contribute to understanding how responsibility, fairness, and power dynamics shape neural alignment that underpins cooperative and moral behavior.