Inter-brain synchronization during coordination of speech rhythm in human-to-human social interaction

TLDR

Human behavioral rhythms synchronize during communication, but how brain rhythms align during speech rhythm coordination between people is unclear. The study used hyperscanning EEG while two participants alternately pronounced alphabet letters, with 20 pairs performing the task before and after each had individually practiced with a machine that produced letters at constant intervals. Human–human speech tasks produced stronger inter‑brain theta/alpha synchrony in temporal and lateral‑parietal regions than human–machine tasks, and both behavioral and neural synchrony increased after participants practiced with the machine, indicating that inter‑brain synchrony is closely tied to speech coordination and may reflect empathy.

Abstract

Behavioral rhythms synchronize between humans for communication; however, the relationship of brain rhythm synchronization during speech rhythm synchronization between individuals remains unclear. Here, we conducted alternating speech tasks in which two subjects alternately pronounced letters of the alphabet during hyperscanning electroencephalography. Twenty pairs of subjects performed the task before and after each subject individually performed the task with a machine that pronounced letters at almost constant intervals. Speech rhythms were more likely to become synchronized in human–human tasks than human–machine tasks. Moreover, theta/alpha (6–12 Hz) amplitudes synchronized in the same temporal and lateral-parietal regions in each pair. Behavioral and inter-brain synchronizations were enhanced after human–machine tasks. These results indicate that inter-brain synchronizations are tightly linked to speech synchronizations between subjects. Furthermore, theta/alpha inter-brain synchronizations were also found in subjects while they observed human–machine tasks, which suggests that the inter-brain synchronization might reflect empathy for others' speech rhythms.