1. From: A double dissociation of the acuity and crowding limits to letter identification, and the promise of improved visual screening
Journal of Vision. 2014;14(5):3. doi: /14.5.3
Figure Legend:
Effect of blur. Threshold spacing is less dependent on acuity (and blur) at greater eccentricity. We measured threshold spacing S versus acuity A for a normal observer (open symbols) and several amblyopes (filled symbols) with various amounts of blur. The normal was tested at several eccentricities; the amblyopes only at fixation. We fit a regression line to each observer at each eccentricity and then plotted the regression line slope (log-log slope of spacing vs. acuity) as a function of padded eccentricity φ + φcrowding. (a) We measured the effect of optical blur. The normal observer (open symbols) was tested at eccentricities of 0° (dotted line), 1.25° (open triangle), and 5° (open square). Amblyopes (filled symbols) were tested at fixation (0°). Each measurement was obtained while the observer was wearing a blurring lens (see Methods) except for the leftmost data point for each observer, which was measured merely with the observer's refractive correction. The dotted regression line is a unit-slope line for a normal observer viewing directly with blur, from Figure 4. A regression is shown for the blur results (with a range of at least one diopter) for each observer and eccentricity tested (see Methods). (b) The lower graph plots the slope of each regression, as a function of the padded eccentricity (φ + φcrowding). For the normal observer, the add-on is fixed φcrowding = 0.45°, and several eccentricities φ are tested. For the amblyopes, eccentricity is zero φ = 0°, and we used the observer's add-on φcrowding from Table 1. Regression lines. (a) SS at 1.25°: log S = log A; SS at 5°: log S = log A; GJ: log S = log A; and AP: log S = log A. (b) Regression line is: Slope = 1.0 – 0.19 (φ + φcrowding).
Date of download: 11/15/2017
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