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Etienne Abassi, Liuba Papeo; The two-body configuration in visual perception. Journal of Vision 2020;20(11):1112. doi: https://doi.org/10.1167/jov.20.11.1112.
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© ARVO (1962-2015); The Authors (2016-present)
Human social nature has shaped visual perception. The relationship between vision and sociality is reflected in the attunement of specialized visual are to social entities such as faces and bodies. We asked whether human vision also exhibits a special sensitivity to spatial relations that reliably correlate with social relations. In general, interacting people are more often situated face-to-face than back-to-back. Using functional MRI (fMRI) and behavioral measures in healthy subjects (Study 1), we showed that visual sensitivity to social stimuli extends to images including two bodies facing toward (vs. away from) each other. In particular, the body-selective extrastriate body area (EBA) responded to facing bodies more strongly than identical, but nonfacing, bodies. In this area, multivariate pattern analysis revealed an accurate representation of body dyads with sharpening of the representation of single-body postures in facing dyads, which suggests an effect of visual context on the perceptual analysis of bodies. Those neural effects were accompanied by an increased cost of inversion (upside-down rotation) on recognition for facing dyads (relative to nonfacing dyads), a behavioral signature of the specialized mechanisms for body (and face) perception. A congruent effect was found selectively in the EBA, when we presented upright vs. inverted facing and non-facing dyads (Study 2): the cost of inversion (reduced activity for inverted vs. upright stimuli) was larger for facing than nonfacing dyads. Thus, spatial relations between multiple bodies are encoded in the same region for body perception and affect the way in which bodies are processed. Particularly, the body-selective cortex is especially sensitive to a spatial configuration encompassing two bodies facing one another, as shown by increased neural activity and increased inversion effect. This two-body configuration in the human visual cortex may represent the perceptual rudiment of the representation of events.
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