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Michael Peer, Russell Epstein; A river runs through it: Brain representations of segmented environments. Journal of Vision 2021;21(9):1828. doi: https://doi.org/10.1167/jov.21.9.1828.
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© ARVO (1962-2015); The Authors (2016-present)
Spatial environments are often segmented into multiple regions or compartments. How is this spatial segmentation represented in the brain? Previous studies have suggested three possible mechanisms: grouping (boundaries warp the global map, making locations in different segments appear more distant than they actually are); schematization (locations are coded with respect to environmental boundaries, in a way that generalizes across segments); and remapping (each segment is represented independently, with no integration into a global map). To test these possibilities, we taught participants the locations of 16 objects within a segmented virtual environment and then used fMRI to assess location codes for these objects. The environment consisted of a virtual courtyard transected by a river that divided it into two geometrically identical segments. Visibility and spatial relations between objects were balanced to be identical within and between segments. After training, participants’ distance estimations and free recall order were affected by the spatial segmentation, suggesting that their mental representations were affected by the presence of the river. Analysis of multivoxel fMRI activity patterns revealed that spatial relations between objects were coded in the hippocampus, occipital place area (OPA) and retrosplenial complex (RSC). Notably, OPA and hippocampus coded schematic representation of the individual segments, such that objects in geometrically equivalent locations within the two segments were represented as being spatially similar, while RSC coded a global map of the environment. We did not find evidence for grouping or remapping. Our findings suggest that spatial segmentation can be induced by topographic feature of the environment even when all parts of the environment are co-visible, and that segmented environments are encoded using a combination of schematic representations of the segments and a global map.
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