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Tiana M. Bochsler, Christopher S. Kallie, Gordon E. Legge, Rachel Gage; Recognition of Ramps and Steps by People with Low Vision. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1910.
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Visual accessibility is the use of vision to travel efficiently and safely through an environment, to perceive the spatial layout of the environment, and to update one’s location in the layout. Legge et al. (J. Vis., 2010) described the effects of lighting, geometry, and surface properties on the recognition of ramps and steps by normally sighted subjects who wore blurring goggles to reduce their acuity. Here we ask whether the results generalize to low vision.
Nine low vision subjects participated-aged 33 to 60-with heterogeneous diagnoses, and acuity from 20/220 to 20/960. They viewed a sidewalk interrupted by one of five possible targets: a single step up or down, a ramp up or down, or flat. In a block of trials, subjects reported which of the five targets was shown, and percent correct was computed. Lighting was from overhead fluorescent bulbs or from artificial windows. Viewing distance was 5, 10 or 20ft from the target. Performance was compared with a group of normally sighted subjects who viewed the targets monocularly through goggles with two levels of blur having effective acuities roughly spanning the low-vision range (20/135 to 20/900).
A plot of overall percent correct vs. acuity revealed that all low-vision subjects outperformed interpolated levels of the goggle wearers. However, the patterns of performance were similar for the two groups. A step up was more recognizable than a step down for both groups. Both groups performed best at the middle (10ft) distance, and the low vision group performed best with window lighting, an effect found in some conditions with the goggle wearers. The order of target performance from best to worst was the same for the low vision group and the lesser blur goggle wearers: step up, step down, flat, ramp down and ramp up.
The overall performance advantage for low-vision subjects over goggle-wearing normals may be due to differences in real-world experience, or possibly to the optical properties of the goggles. Despite this difference, the qualitative effects of distance, lighting and target type were similar for the normal and low-vision groups.
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