Visual Detection of Detectable Warning Materials by Pedestrians with Visual Impairments - Final Report

1.7 Procedure

The study utilized a full factorial, repeated-measures design in which participants viewed each of the 13 detectable warnings against each of the 4 sidewalks for a total of 52 trials. Two “blank” trials were also inserted for each of the sidewalks (except the brick sidewalk) for a grand total of 58 trials. Participants completed all trials on a particular sidewalk before moving on to the next side walk. The order in which sidewalks were viewed was randomized for each participant, as was the order of the detectable warnings (and blank trials) viewed on each sidewalk. Participants were tested individually in sessions lasting 1.5 to 2.5 hours.

The purpose and general activities involved in the study were explained to participants during initial telephone screening. Consent forms were printed in a large font size and sent to participants via mail or e-mail (whichever was preferred).

1.7.1 Introduction and Vision Testing

Upon arrival at Westat, participants were guided to the vision testing room. Participants were escorted at all times by an experimenter who had received training from an orientation and mobility specialist. The experimenter first read the consent form aloud to participants who had not had the opportunity to read it themselves and then collected signed consent forms. Next, participants were asked to describe their visual condition, the functionality of their vision, and their use of mobility aids. Three separate vision tests were performed to assess participants’ visual acuity, contrast sensitivity, and color vision. For these tests, participants were allowed to view the charts binocularly and to use head or eye movements necessary to read as many letters or symbols as possible. Details on the vision testing procedures are given in Appendix E. No formal assessments of each participant’s visual fields were conducted due to time constrains, however based on self- reports, the study sample included participants with small, medium, and large visual field losses.

The experimenter guided participants to the outdoor testing site and familiarized them with the site layout. Participants were given a small sample piece of detectable warning material to see and feel, then were shown examples of a detectable warning and a blank on a sidewalk. The experimenter then described the study procedures and guided participants through a practice trial before beginning the study trials.

1.7.2 Visual Detection Distance

Each trial began with the participant standing 7.9 m (26 ft) from the front edge of the detectable warning. The 7.9 m (26 ft) viewing distance was chosen to approximate the width of a residential street. Participants began facing away from the sidewalk to allow a second experimenter to lay down a detectable warning (or blank). When the detectable warning was in place, the participant turned around and reported to the experimenter whether he/she was confident that there was a detectable warning on the target sidewalk. If the detectable warning was not seen from 7.9 m (26 ft) away, the participant was instructed to walk slowly toward the sidewalk and to stop immediately if he/she became confident that there was a detectable warning (and not a blank) present. If the participant came within 2.4 m (8 ft) of the detectable warning and could not confidently say that a detectable warning was present, the trial was ended.

1.7.3 Color Naming, Conspicuity Rating, and Other Comments

If the participant was able to see the detectable warning from at least 2.4 m (8 ft) away, the experimenter guided the participant to the 8-foot line to ask two more questions. First, the participant was asked what color or pattern they saw on the detectable warning. Second, the participant was asked to rate the likelihood that the detectable warning would attract his/her attention on that particular sidewalk (conspicuity). A rating scale of 1 to 5 was used where 1 meant (the detectable warning is very unlikely to attract my attention on this type of sidewalk) and 5 meant (the detectable warning is very likely to attract my attention on this type of sidewalk).

If the participant did not see the detectable warning from 2.4 m (8 ft), a conspicuity rating of zero was assigned by the experimenter. Although additional comments were not solicited, the experimenter also recorded any relevant comments that the participant provided about the detectable warnings, such as, “looks like a cement patch.”