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Size coding of real-world objects in human dorsal cortex
AuthorHoller, Desiree E.
AdvisorSnow, Jacqueline C.
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Neural object representations were discovered in human posterior parietal cortex (PPC) almost a decade ago  yet the functional contribution of this area to object perception remains poorly understood . Classically, visual object coding in human ventral and dorsal cortex has been studied using images [3-7], but two-dimensional (2D) images do not convey exact egocentric distance or size information, and neither 2D nor three-dimensional (3D) stereoscopic images of objects afford grasping and interaction. Unlike ventral cortex, object representations in PPC are especially sensitive to 3D shape [8, 9], and are proximal to hand orientation and pre-shaping areas [10-12] and to egocentric spatial maps of the visual field , making these representations uniquely positioned to code the size and shape of graspable objects. Here, we isolated the contribution of dorsal cortex to size and shape processing by studying object recognition in patients with visual form agnosia following bilateral damage to shape-processing areas of ventral cortex. The patients were asked to identify objects, whose size was congruent or incongruent with typical real-world size (RWS), presented in different display formats (real objects, 2D and 3D images). While recognition of 2D and 3D images was extremely poor, real object recognition was surprisingly preserved, but only when physical size reflected RWS. Analogous display format and size manipulations had no effect on recognition of basic geometric shapes that lacked RWS associations. These findings reveal, for the first time, size-coding of real objects in dorsal cortex and highlight the importance of using real-world stimuli to understand perception.