Evaluating the Visual Accessibility of Stairs in Public Spaces

Abstract

Approximately 14 million Americans aged 12 years or older have self-reported visual impairment, according to the Center for Disease Control and Prevention. Visual impairment has a high prevalence in old age, hence, mobility hazards, such as stairs, pose a major challenge to this group. This challenge is not well recognized by architects while designing indoor steps. In this project, I proposed that there are certain factors, such as low contrast, and poor contrast, in the design of steps and their interactions that make their visibility difficult. HDR images of stairs in university buildings, which aim to capture the contrast sensitivity of the human eye, are processed using a pre-programmed MATLAB code. The stimuli factors included in the images are distance from the stairs, natural/artificial lighting in the space, and viewpoint (from top/bottom). Images are filtered to four levels of reduced visual acuity, simulating the corresponding levels of visual impairment. Human subjects were asked to analyze the visibility of the filtered images using a rating test. Their judgments were then analyzed to determine which photographs were rated most visible. This would help decide factors in the design of the stairs that were most helpful in improving the detectability of the steps. Through this analysis, one of the main factors that affect subject-rating was the distinction between individual steps through the contrast between the rise of each step and the surface. Higher the contrast, higher was the subject-rating. Another observation was that, at reduced acuity levels, as the distance from the stairs decreased, visibility increased. This proposes ideas for improving the design of stairs.