Recognition of ramps and steps by people with low vision.

Purpose: Detection and recognition of ramps and steps are important for the safe mobility of people with low vision. Our primary goal was to assess the impact of viewing conditions and environmental factors on the recognition of these targets by people with low vision. A secondary goal was to determine if results from our previous studies of normally sighted subjects, wearing acuity-reducing goggles, would generalize to low vision.

Methods: Sixteen subjects with heterogeneous forms of low vision participated-acuities from approximately 20/200 to 20/2000. they viewed a sidewalk interrupted by one of five targets: a single step up or down, a ramp up or down, or a flat continuation of the sidewalk. Subjects reported which of the five targets was shown, and percent correct was computed. The effects of viewing distance, target-background contrast, lighting arrangement, and subject locomotion were investigated. Performance was compared with a group of normally sighted subjects who viewed the targets through acuity-reducing goggles.

Results: Recognition performance was significantly better at shorter distances and after locomotion (compared with purely stationary viewing). The effects of lighting arrangement and target-background contrast were weaker than hypothesized. Visibility of the targets varied, with the step up being more visible than the step down.

Conclusions: The empirical results provide insight into factors affecting the visibility of ramps and steps for people with low vision. The effects of distance, target type, and locomotion were qualitatively similar for low vision and normal vision with artificial acuity reduction. However, the effects of lighting arrangement and background contrast were only significant for subjects with normal vision.