We take what we see, hear, smell and feel for the reality. However, as neuroscientists, we know that this reality, that is, our perceptual world, is in fact made up by the brain from the processing of the nerve impulses coming from receptors. Ancient Greeks used to think that this perceptual world, sometimes called our 3D movie (Chalmers), is emitted and has its own physical nature. Given how real the 3D movie looks to us, it is still difficult today to consider that all we would be dealing with would be patterns of brain activity The present study thus aimed at testing whether the perceptual world could have some physical existence in addition to that of the neural patterns responsible for it. To achieve that goal, we tried to see whether brains could be sensitive to the 3D movie of others. This, admittedly unusual, operational hypothesis was based on two assumptions. First, brains are sensitive to the 3D movie, as our experience includes reactions to our perceptual world. Second, the physicality at stake does not differ across individuals. We recorded the event-related brain potentials (ERPs) evoked by stimuli of the international affective picture system in pairs of closely-related participants. Most importantly, they could neither see the stimuli simultaneously presented to their partners nor their reactions to them. As in Bouten et al. (2015), around 400 ms after the onset of the stimuli, ERPs started being more positive in inconsistent conditions. Namely, when the two subjects of each pair were presented with the same stimulus whereas they were told it would be a different one and vice-versa (i.e., different-stimuli expected to be same). ERPs were less positive when the two subjects of a pair were presented with the same stimuli and were told they were the same and conversely (i.e., different-stimuli expected to be different). The same experiment was then run in pairs of strangers. No significant effect of consistency on ERPs was observed even though participants could, this time, see, in the very periphery of their visual field, the reactions of their partner to the stimuli. We thus use the results of both studies to support a new version of the emission theory of consciousness and to suggest that the sensitivity to the perceptual world of others may depend on their prior familiarity with it.Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted:
The most robust and clear biological index differentiating persons with schizophrenia from healthy controls is the drastic reduction of the amplitude of their P300b event-related brain potential (ERP). However, the cause of that reduction remains obscure. Nevertheless, the P300b belongs to the family of the late posterior positivities (LPPs) which are closely related to the consciousness of the meaning of the stimulus in the task for the participants themselves (e.g., the: I am seeing the target stimulus for which I have to respond). The fragmentation of the self present in schizophrenia, could thus be the cause. If this were true, then P300bs should be somewhat reduced in healthy participants when their self representations are temporarily and minimally fragmented. We tested this hypothesis by using the innocuous fragmentation of the self that occurs in virtual reality (VR). There, participants can have a fragment of their self in an avatar they feel embodied in, within a VR room, while having another fragment of their self in their real body in the real room where they know they are. Our participants were thus equipped with a head mounted display in which they viewed a virtual room where a female humanoid avatar was facing them. She was lifting her right hand in synchrony with the participants, in order to induce in them a feeling of embodiment. Stimuli were a frequent green- and a rare red-disk, the oddball stimulus, occurring over the right hand of the avatar. Participants had to perform a Go/NoGo task, lifting their right hand to the frequent green disk and repressing this action for the oddball red disk. In the syncMove block of trials the avatar was lifting her right hand synchronously with the participant, disturbing her self representation as confirmed by the debriefing session. In the noMove block, the avatar remained immobile. In the classic block, only the red and the green disk were displayed on a monochrome background, neither the room nor the avatar were shown. As predicted, P300bs were found to be smaller in the syncMove block than in the noMove- and the classic-block in participants who had the classically large P300b oddball effect between ERPs to the frequent and those to the rare stimuli. Reduced P300bs of schizophrenia could thus be partly due to self fragmentation. Results may also open an avenue of research to the functional significance of LPPs and the content of the consciousness indexed by these potentials.
The early and preconscious processing of stimuli that are meaningful in everyday life includes systematical activations of many semantic, emotional and motor representations. Inhibitions should then occur in order to select, among these primed representations, those that are consistent with the context. Even in a lab this context is social, as it typically consists of the experimenter and of the instructions and stimuli (s)he provides. Three recent N400 studies confirm this social view of experimental settings by showing that socially driven processes affect what was primed by prior stimuli. The small amplitudes of the N400 event-related potentials (ERPs) elicited by stimuli preceded by semantical primes were found to be enhanced by the mere presence of a person next to participants when they know this person did not have the semantic primes. It thus seems that N400 processes inhibit what these primes have activated so that participants can also have the perspective of the uninformed person. This inhibition interpretation implies that N400s should be notably reduced when nothing allows to determine what should be inhibited, that is, when the social context is not defined and when task’s instructions require minimal inhibition. We tested this prediction by having a stranger next to participants (n=29) and by presenting meaningful unpredictable images in a simple memorization task. As foreseen, N400s were small. They were enhanced by definable social contexts, that is, in participants alone with the experimenter (n=30) and in those with a friend (n = 36). The amplitudes of the N300s were also enhanced. A second experiment revealed that these N300 and N400 enhancements were larger for friends who felt in the presence of their partner during most of the experiment. As to the late posterior positivities (LPPs) immediately succeeding the N400s, they were found to be larger in the unknown social context of the first experiment, suggesting that more information ended up being placed into the working memory when inhibitions could not occur. These results are compatible with a serial 3-stages framework of the processing of stimuli meaningful in everyday life. Early and broad systematic activations (priming) would be followed by automatic late selections done according to the social-context and then, by the participant’s consciousness of the meanings of the stimulus in this context. As inadequate late selections would cause impairments of social and cognitive behaviors, the present results could have implications for psychiatric disorders, such as autism and schizophrenia.
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