Neurophysiological synchrony as an emergent performance marker of multi-human-robot team effectiveness.

Most human-robot interaction research focuses on dyadic interactions, yet real-world applications require multi-human-robot teams (mHRTs). While surveys, communication metrics, and performance capture team processes, neurophysiological synchrony between human dyads offers a promising marker of team dynamics. This study investigated how robot reliability shapes trust, coordination, and neurophysiological synchrony in mHRTs, and whether neurophysiological measures predict mission outcomes beyond traditional assessments. Twenty-three teams (two humans, one robot) completed search-and-rescue missions under reliable and unreliable robot conditions. Multimodal data included inter-brain synchrony, physiological synchrony, trust, behavioral coordination, and performance metrics. Robot unreliability reduced trust in the robot but not between humans. Paradoxically, teams with unreliable robots performed better through adaptive behaviors. Physiological synchrony increased significantly under unreliable conditions. Neural synchrony in the frontal cortex decreased with robot unreliability, whereas temporoparietal junction synchrony remained stable. Neurophysiological synchrony explained additional variance (ΔR2=0.195) in wayfinding performance beyond trust and behavioral measures (R2=0.456).