Seeing steps and ramps with simulated low acuity: impact of texture and locomotion

Detecting and recognizing steps and ramps is an important component of the visual accessibility of public spaces for people with impaired vision. The present study, which is part of a larger program of research on visual accessibility, investigated the impact of two factors that may facilitate the recognition of steps and ramps during low-acuity viewing. Visual texture on the ground plane is an environmental factor that improves judgments of surface distance and slant. Locomotion (walking) is common during observations of a layout, and may generate visual motion cues that enhance the recognition of steps and ramps.

In two experiments, normally sighted subjects viewed the targets monocularly through blur goggles that reduced acuity to either approximately 20/150 (mild blur) or 20/880 Snellen (severe blur). The subjects judged whether a step, ramp, or neither was present ahead on a sidewalk. In the texture experiment, subjects viewed steps and ramps on a surface with a coarse black-and-white checkerboard pattern. In the locomotion experiment, subjects walked along the sidewalk toward the target before making judgments.

Surprisingly, performance was lower with the textured surface than with a uniform surface, perhaps because the texture masked visual cues necessary for target recognition. Subjects performed better in walking trials than in stationary trials, possibly because they were able to take advantage of visual cues that were only present during motion.

We conclude that under conditions of simulated low acuity, large high-contrast texture elements can hinder the recognition of steps and ramps, whereas locomotion enhances recognition.