Beyond unison: auditability and partner-differentiated cooperation in joint music-making, with body percussion as a test case

Interpersonal entrainment is widely held to promote prosocial behavior by dissolving self–other boundaries, yet meta-analytic effects are moderate and shrink markedly when experimenters are blind to the condition. The author proposes a complementary mechanism with a deliberately minimal core: coordinated music-making makes each participant's contribution auditable , generating person-specific information about demonstrated reliability, and this information subsequently produces partner-differentiated cooperation. Auditability differs from generic observability in that contributions are evaluated in real time, within an interdependent task, against a shared standard fixed in advance, namely, meter. The author separates its constitutive conditions (detection and multimodal attribution) from its scope condition (publicity) and from the conditions that make the evidence diagnostic of commitment rather than skill (non-substitutability, visible cost, interference). They argue that the relevant evidence is maintenance of one's part under interference; specify what participants learn that observers cannot; distinguish public availability, mutual recognition, and common knowledge; and give a simple treatment of how reliability estimates converge as group size grows. The two accounts diverge: fusion predicts prosociality undifferentiated within the group, whereas auditability predicts cooperation differentiated by demonstrated reliability. Body percussion is treated as a convenient test case, not as a privileged medium. The author states the core hypothesis, its necessary assumptions, auxiliary and medium-specific hypotheses, and extensions separately and lists which outcomes would falsify the core and which would revise only an extension.