Seeing Steps and Ramps with Simulated Low Acuity

Abstract

Purpose 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. Methods In two experiments, normally sighted subjects viewed the targets monocularly through blur goggles that reduced acuity to either approx. 20/150 Snellen (mild blur) or 20/880 (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. Results 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. Conclusions We conclude that under conditions of simulated low acuity, large, high-contrast texture elements can hinder the recognition of steps and ramps while locomotion enhances recognition.

Recognition of Ramps and Steps by People with Low Vision

“…Performance in walking and stationary trials. Subjects with low vision are compared to those with normal vision wearing blur goggles in Bochsler et al 11 Error bars represent 61 SE. FIGURE 6.…”

“…This might be especially significant for people with very low acuity because it is well known that contrast sensitivity for patterns composed of low spatial frequencies is enhanced by abrupt temporal onsets or offsets. 16 See Bochsler et al 11 for a more detailed description of motion cues.…”

“…Walking and stationary trials were randomly interleaved, with four trials per target in each condition, for a total of 40 trials. Bochsler et al 11 used the same paradigm to measure the influence of locomotion on the performance of normal subjects with acuity-reducing goggles. They addressed the difference in time per trial for walking and stationary trials and concluded that it was unlikely to influence the results.…”

“…In a subsequent study using similar methods, Bochsler et al 11 asked whether two additional visual factors-surface texture and self-locomotion-would enhance the recognition of ramps and steps under low-acuity viewing. Contrary to expectation, a coarse texture pattern on the ground plane detracted from performance.…”

“…These factors include target-background contrast and lighting arrangements, and also viewing conditions such as distance to target. 10,11 A major aim of the present study was to determine if these results generalize to people with low vision. A long-term goal of our research on visual accessibility is to provide a principled basis for guiding the design of safe environments for the mobility of people with low vision.…”