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shahin nasr, Roger Tootell; Columnar Neural Mechanisms Underlying Vertically Asymmetric Global Visual Processing. Journal of Vision 2018;18(10):122. doi: 10.1167/18.10.122.
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© ARVO (1962-2015); The Authors (2016-present)
Global visual processing refers to the detection of large scale coherences and low spatial frequency (SF) cues that comprise a meaningful gestalt. Humans perceive stimuli more globally when presented within the lower (rather than the upper) visual field. This vertical asymmetry is likely due to higher ecological relevance of global visual processing of near (within arm's reach) compared to farther objects (Previc, 1990) that, in natural scenes, are more frequently present within the lower rather than the upper visual field (Yang and Purves, 2003). However, neural mechanisms that underlie this phenomenon are still mostly unknown. In this study, we used high-resolution fMRI (0.8-1.0 mm isotropic voxels), collected in an ultra-high field (7T) scanner, to study global processing in depth sensitive (disparity-selective) cortical columns within human visual areas V2, V3 and V3A (n=10). Using this technique, we measured activity evoked within these columns by retinotopically-equated near vs. far stimuli, generated by disparity-varying random dot stereograms. Our findings indicated that the extent of vertical asymmetry in global visual processing (measured behaviorally) varies across individuals correlated with the level of fMRI response evoked by near (but not far) stimuli in their V3A. To better clarify V3A role in global processing, we compared the fMRI response to a wide range of 1D and 3D SFs in near- and far-preferring clusters within disparity-selective columns. We found that, in V2, V3 and V3A, near-preferring clusters (compared to far-preferring ones) responded more selectively to low SFs (< 0.5 cycle/degree), important for global visual processing. However, compared to V2 and V3, the preferred SF was significantly lower in V3A disparity-selective columns, suggesting a stronger link between the vertically asymmetric global processing and the function of near-preferring clusters within V3A compared to V2 and V3. These findings highlight the importance of fine-scale cortical structures in controlling human behavior.
Meeting abstract presented at VSS 2018
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