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Sarah Rosen, Ramakrishna Chakravarthi, Denis G. Pelli; Nasotemporal asymmetry of acuity and crowding. Journal of Vision 2008;8(6):972. doi: 10.1167/8.6.972.
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Peripheral acuity is thought to reflect ganglion cell density. The critical spacing of crowding is thought to reflect the (reciprocal of) cortical magnification factor. At large eccentricities, beyond 20 degrees, nasal retina has a much higher acuity than temporal retina (Anderson and Mullen, 1991). With binocular viewing, left and right visual fields are symmetric but we wondered whether the critical spacing of crowding, tested monocularly, would show an asymmetry. An asymmetry would be surprising because dichoptic crowding experiments have indicated that eye of origin doesn't matter. We measured the critical spacing at an eccentricity of 25 degrees for 5 deg target and flanker letters (black, uppercase Courier) on the horizontal meridian. The flanker was displaced from the target either inward (toward the fovea) or outward (away from the fovea). We also measured acuity for identifying an isolated target letter and found both subjects to have an acuity ratio of 1.5. The mean ± standard error of the ratio of critical spacings for both conditions for two observers is 1.5 ± 0.2 deg. Thus crowding tracks acuity and eye of origin does matter. Critical spacing for crowding at a given location in the visual field depends on which eye is used.
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