Attentional engagement strengthens joint agency: evidence from intra-brain, inter-brain, and behavioural signals via EEG hyperscanning

Joint actions are often accompanied by a sense of joint agency, i.e., a sense that co-performers are acting together to produce the joint action and its corresponding consequences. Recent evidence suggests that inter-brain neural synchrony (INS) may play a role in determining people's sense of joint agency. However, researchers have yet to investigate whether individual-level neural signals also contribute to people's sense of joint agency. The current study therefore employed EEG hyperscanning to investigate the contributions of both individual and inter-brain neural signals, as well as behavioural coordination, to joint agency. Partners used electronic music boxes to synchronize tone sequences to produce either musical duets (familiar melodies with supporting accompaniment) or constant pitch sequences (pitches spaced a twelfth apart). Both partners rated their sense of joint agency after each trial. EEG analyses focused on neural activity related to auditory processing, isolated using Independent Component Analysis (ICA) for spatial source separation. Duets elicited stronger joint agency compared to constant pitch sequences, regardless of how well synchronized they were. Duets also elicited larger auditory ERPs (N1 and P2 components reflecting attentional engagement) and greater INS of auditory activity in the beta frequency band. Furthermore, auditory ERPs partially mediated the relationship between sequence type and joint agency, and fully mediated the relationship between sequence type and INS. These findings indicate that attentional engagement strengthens joint agency and that individual auditory processing provides a more direct neural correlate of joint agency than inter-brain coupling of auditory activity.