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Edgar Chan, Oliver Baumann, Mark Bellgrove, Jason B. Mattingley; Extrinsic reference frames modify the neural encoding of object locations during active spatial navigation. Journal of Vision 2011;11(11):862. doi: https://doi.org/10.1167/11.11.862.
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The ability to form object-to-object spatial representations is an important component of successful spatial navigation. Retrieval of object-location information is more efficient and accurate when an observer's heading within an object-array is aligned with an extrinsic reference frame (e.g., parallel to the sides of a rectangular field), than when it is misaligned (e.g., a heading that runs oblique to the field's side). Whether this alignment effect is due to stronger stored representations for aligned views or differences in egocentric-transformation processes during retrieval is unknown. We used functional magnetic resonance imaging (fMRI) to address this question. In an initial encoding phase conducted outside the scanner, participants learned the layout of an object array in an active virtual-navigation paradigm. A square mat positioned on the floor of the virtual arena acted as the extrinsic reference frame. A subsequent retrieval phase was conducted in the scanner, during which participants performed a spatial judgment task that required them to imagine orientations of the learned object-array that were either aligned or misaligned with the sides of the mat. Consistent with previous findings, participants responded faster and more accurately when the imagined orientation was aligned as opposed to misaligned with the extrinsic reference frame. Analysis of the fMRI data also revealed significant differences in brain activity between the two conditions. For the Aligned>Misaligned contrast, significantly greater activity was observed bilaterally in the inferior occipital, inferior and middle temporal, and fusiform gyri. For the Misaligned>Aligned contrast, significantly greater activity was found bilaterally in dorsolateral prefrontal and anterior cingulate cortex, and in the right anterior prefrontal and anterior insular cortex. The activation of distinct neural circuits for the aligned and misaligned conditions during object-location retrieval suggests that extrinsic reference frames modulate the way in which object-location information is encoded during active spatial navigation.
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