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Gennadiy Gurariy, Timothy J Vickey, Adam S Greenberg; Visuospatial Object-Based Warping is Detectable in Early Visual Cortex. Journal of Vision 2020;20(11):1421. doi: https://doi.org/10.1167/jov.20.11.1421.
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In vision, objects constitute high-level percepts resulting from the spatial grouping of sensory information. Interestingly, it has been demonstrated that space within objects can appear systematically warped: items enclosed within an object are perceived further apart relative to equidistant items not enclosed within an object (Vickery & Chun, 2010). Here, we use functional magnetic resonance imaging (fMRI) to investigate the neural representation of object-based warping (OBW). First, participants adjusted perceived distances between two letters so as to match two reference letters either contained within an object, or not. This allowed us to compute the perceived “warping” of letter spacing due to OBW. Next, participants performed a discrimination task among four letters while fMRI data were collected in 3 conditions: (1) two letters were enclosed within an object, (2) two letters appeared without an object at the same visual field locations as in condition 1, and (3) two letters appeared without an object at the “warped” distances (calculated from behavioral data). Additionally, using a spatial position localizer, two regions of interest were defined corresponding to the retinotopic locations of letters within an object (real positions; conditions 1 & 2), and two regions corresponding to the “warped” positions (condition 3). Using neural activity extracted from each region, an MVPA classifier was trained on the difference between the two no-object conditions (conditions 2 & 3) and tested on the object-present condition (condition 1). Within ROIs corresponding to real spatial positions, the object condition was classified as “real” in V1 and “warped” in V2-V3. Within ROIs corresponding to the warped spatial positions, the object condition was classified as “warped” in V1-V3. This evidence of OBW in early visual cortex is likely driven by feedback from higher-level areas and suggests a fundamental change to visual perception caused by the presence of a simple object.
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