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Anirvan Nandy, Bosco Tjan; Crowding and cortical reorganization at and around the PRL: model and predictions. Journal of Vision 2010;10(7):1351. doi: 10.1167/10.7.1351.
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© ARVO (1962-2015); The Authors (2016-present)
Visual crowding is a ubiquitous phenomenon in peripheral vision and manifests itself as the marked inability to identify shapes when targets are flanked by other objects. It presents a fundamental bottleneck to object recognition for patients with central vision loss. Such patients typically use a stable location in their peripheral retina for fixation for a given task. This location is usually very close to the central scotoma and is known as the preferred retinal locus (PRL). Preliminary studies (Chung & Lin, 2008, ARVO) have shown that the crowding zone measured at the PRL does not exhibit the marked anisotropy that is a hallmark of crowding in the normal periphery (Toet & Levi, 1992). This suggests that there is a process of cortical reorganization that reshapes the crowding zone at the PRL. However, little is known about the underlying causes and the temporal trajectory of the reorganization process. Recently we have proposed a computational model that explains crowding as a consequence of inappropriate image statistics that drive the lateral (long-range horizontal) connections underlying the normal peripheral visual field (Nandy & Tjan, 2009, SfN). The temporal overlap of spatial attention and subsequent fovea-centric saccadic eye movements distort the image statistics to produce the radial anisotropy. By adding to our model the central scotoma and the PRL measured from a patient, we show that the altered image statistics due to the temporal overlap of spatial attention and PRL-centric eye movements would drive the crowding zone at the PRL to being isotropic. We also delineate the developmental time course from pre-scotoma anisotropy to post-scotoma isotropy as a function of exposure to the post-scotoma statistics. Further, our model predicts that the crowding zone at an intact non-PRL location would also undergo reorganization from anisotropy pointing toward the fovea (pre-scotoma) to anisotropy pointing toward the PRL (post-scotoma).
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