Unlocking information alignment between interacting brains with EEG hyperscanning

Social interactions shape our perception of the world as the people we interact with, and groups we belong to, influence how we interpret incoming information. Alignment between interacting individuals’ sensory and cognitive processes plays a critical role in facilitating cooperation and communication in everyday joint activities. However, despite recent advances in hyperscanning techniques to measure the brain activity of multiple people simultaneously, the neural processes underlying this alignment remain unknown. Here, we leveraged Representational Similarity Analysis (RSA) with electroencephalography (EEG) hyperscanning data to measure neural representations and uncover the emergence of information alignment between interacting individuals’ brains during joint visual categorisation. We recorded EEG from 24 pairs of participants sitting back-to-back while they performed a 4-way categorisation task based on rules they first agreed upon together. The results revealed significant interbrain information alignment as early as 45 ms after stimulus presentation, lasting over hundreds of milliseconds. Importantly, early alignment between brains arose between 45 and 180 ms regardless of whether participants performed the task together or were randomly matched up a posteriori to form pseudo pairs, whereas alignment after 200 ms was only present for real pairs who previously formed the categories together. This result distinguishes alignment that was socially induced by pre-agreed and shared interpretation of the stimuli from alignment that was purely evoked by shared sensory responses due to participants seeing the same visual input. In addition, our results showed that socially induced alignment was an active and dynamic process, which strengthened over time with practice and reinforcement of shared agreements, but appeared to remain largely task specific with no transfer during passive viewing of the same stimuli. Together, these findings highlight distinct sensory evoked and socially induced processes underpinning human perception and interbrain information alignment during social interactions that can be effectively captured and disentangled with Interbrain RSA.