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Adam Messinger, Benjamin Jung, Caleb Sponheim, Leslie G Ungerleider; fMRI mapping of retinotopy using face and object stimuli in rhesus monkeys. Journal of Vision 2019;19(10):261a. doi: https://doi.org/10.1167/19.10.261a.
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Visual processing in the primate brain consists of a ventral visual stream that primarily processes the shape of visual stimuli (the “what” stream) and a dorsal visual stream that primarily processes the location of those stimuli (the “where” stream). Early visual areas have been shown to be retinotopically organized, with different portions of the visual field spatially mapped to the cortex. Such retinotopy becomes less apparent in later stages of the ventral visual stream, where many neurons have large receptive fields. These later ventral stream areas have been shown using fMRI to contain category-selective regions (e.g. face patches). It is unclear the extent to which these later stages of the ventral visual stream and category-selective regions retain information about stimulus location. Using a block design, we measured fMRI responses in rhesus macaques to images of monkey faces and objects presented in each of four quadrants of the visual field during a central fixation task. Stimuli were 7×7 degrees of visual angle and presented at 6 degrees of eccentricity. We evaluated responses in anatomically-defined ventral visual stream areas. Early visual areas (V1–V4) responded retinotopically, generally preferring the contralateral visual field, with more inferior regions preferring the upper visual field and more superior regions preferring the lower visual field. Later stages of the ventral visual stream retained a contralateral preference and voxels responding significantly more to stimuli in the lower quadrants than the upper quadrants were more common than the reverse. This result indicates that some information about stimulus location is retained even in the later stages of the ventral stream, where complex shapes such as faces and objects are processed. The bias for lower-field stimuli suggests that face and object recognition may be more accurate or efficient in the lower relative to the upper visual field.
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