Conditions for Inter-brain Synchronization in Remote Communication: Investigating the Role of Transmission Delay

Inter-brain synchronization (IBS), the alignment of neural activities between individuals, is a fundamental mechanism underlying effective social interactions and communication. Prior research has demonstrated that IBS can occur during collaborative tasks and is deeply connected to communication effectiveness. Building on these findings, recent investigations reveal that IBS happens during remote interactions, implying that brain activities between individuals can synchronize despite latency and physical separation. However, the conditions under which this synchronization occurs or is disrupted in remote settings, especially the effect of latency, are not fully understood. This study investigates how varying transmission latency affects IBS, in order to identify thresholds where synchronization is disrupted. Using electroencephalography measurements quantified through Phase Locking Value -- a metric that captures synchronization between brainwave phases -- we first confirm synchronization under face-to-face conditions and then observe changes in IBS across remote communication scenarios. Our findings reveal that IBS can occur during remote collaboration, but is critically dependent on transmission delays, with delays exceeding 450 ms significantly disrupting synchronization. These findings suggest that IBS may serve as a key indicator of communication quality in remote interactions, offering insights for improving remote communication systems and collaboration.