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Gabrielle Roddy, Wael Chanab, Rick Gurnsey; Symmetry and Crowding Across the Visual Field. Journal of Vision 2010;10(7):1329. doi: 10.1167/10.7.1329.
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© ARVO (1962-2015); The Authors (2016-present)
Background: There is a consensus that crowding is a property of peripheral (but not foveal) vision and that crowding zones are elliptical and oriented towards the fovea. However, Latham and Whitaker (1996) found evidence of crowding at fixation and suggested that multiple linear magnifications were required to explain the changes in crowding from fixation to the periphery. Past studies of crowding have involved gratings (e.g., Latham & Whitaker, 1996, OPO) or alphanumeric characters (e.g., Cavanagh, 2002, VR; Pelli et al. 2007, JoV). Here we ask whether the basic characteristics of crowding apply to biologically relevant stimuli; specifically, symmetry. Furthermore, we ask whether multiple linear magnifications explain the changes in crowding from fixation to the periphery. Method: We measured size thresholds for target/crowder separations of 1.25 to 8.00 times target size, as well as a no-crowder condition, in a symmetry discrimination task. Thresholds were measured with the target at fixation and 8° below or to the right of fixation. In one condition the crowders flanked the target vertically and in another they flanked the target horizontally. In all cases we plotted target size at threshold as a function of separation at threshold. Results: At fixation, size thresholds were independent of target/crowder separation. At all other eccentricities threshold size decreased as separation increased until asymptote was reached, at which point size thresholds were independent of separation. As well, crowding was stronger when flankers were presented parallel to the fixation-to-target axis, consistent with the suggested structure of crowding zones. Conclusions: Consistent with previous literature it appears that there is a qualitative difference in crowding across the visual field; symmetry appears to behave like previously studied stimuli. Therefore, contrary to our expectations, and previous data (Latham & Whitaker, 1996), multiple linear magnifications seem inadequate to characterize the data.
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