Head movements while crossing streets: effect of vision impairment.

摘要

BACKGROUND: Crossing the street is an activity that requires gathering information over a large area. The challenge in safely crossing a street is to acquire the necessary information for a decision of when to cross within a limited window of time. The purpose of this study was to compare the head movement behavior of visually impaired pedestrians with fully sighted pedestrians at two types of complex intersections: a plus intersection and a roundabout. METHOD: We measured the head movement behavior of 12 subjects with normal vision, 11 subjects with age-related macular degeneration (AMD), and 10 subjects with glaucoma as they approached and crossed at the two intersections. The primary measures were the percentage of time the head was directed to the left, center, or right and the frequency of head turns. We compared measures across groups and relative to three criteria of head movement behavior for maximizing street-crossing safety. RESULTS: Crossing the street can be divided into three phases: walking to the curb, standing at the curb, and crossing the street. We found that while moving, the majority of subjects directed their head to the center. This was true at the plus intersection and roundabout. Group differences were found in the frequency of head turns at the plus intersection, with the AMD pedestrians having a lower frequency of head turns compared with the fully sighted pedestrians. However, the frequency of head turns increased for all the groups during the last 4 seconds before crossing, with the frequency being the greatest during the last second. Numerous subjects had head movements consistent with pedestrian safety, although there were subjects in each group who failed to demonstrate maximum safety. More of the visually impaired pedestrians exhibited less safe head movement behavior than the fully sighted pedestrians. CONCLUSIONS: The effects of visual impairment on head movement behavior were associated with pedestrian safety at critical moments in the street-crossing process. Mobility training programs aimed at teaching safe head movement behavior for street crossing could help to increase the safety of visually impaired pedestrians.