Finding indexes of spontaneous brain-to-brain communications when looking for a cause of the similarity of qualia assumed across individuals.

Qualia, the individual instances of subjective conscious experience, are private events. However, in everyday life, we assume qualia of others and their perceptual worlds, to be similar to ours. One way this similarity is possible is if qualia of others somehow contribute to the production of qualia by our own brain and vice versa. To test this hypothesis, we focused on the mean voltages of event-related brain potentials (ERPs) in the time-window of the P600 component, whose amplitude correlates positively with conscious awareness. These ERPs were elicited by stimuli of the international affective picture system in 16 pairs of friends, siblings or couples going side by side through hyperscanning without having to interact. Each member of each pair faced one half of the screen and could not see what the other member was presented with on the other half. One stimulus occurred on each half simultaneously. The sameness of these two stimuli was manipulated as well as the participants' belief in that sameness. ERPs were more negative over left frontal sites and P600 amplitudes were minimal at midline sites when the two stimuli were, and were believed to be, different, suggesting that this belief could filter others' qualia. ERPs were less negative over left frontal sites and midline P600s were a bit larger when the two stimuli were, and were believed to be, the same, suggesting some mutual enrichment of the content of awareness in conditions of real and assumed similarity. When stimuli were believed to be the same but actually differed, P600s were greater over a large number of sites, suggesting greater enrichment in conditions of qualia difference and assumed similarity. P600s were also larger over many sites, when stimuli were believed to differ but were identical, suggesting that qualia similar to ours could pass the "believed-different filter".