Gaze behavior during navigation with reduced acuity.

Navigating unfamiliar indoor spaces while visually searching for objects of interest is a challenge faced by people with visual impairment. We asked how restricting visual acuity of normally sighted subjects would affect visual search and navigation in a real world environment, and how their performance would compare to subjects with naturally occurring low vision. Two experiments were conducted. In the first, 8 normally sighted subjects walked along an indoor path, looking for objects placed at unpredictable intervals to the left and right of the path, and identified single letters posted on the objects. A head-mounted eye tracker was used to assess their gaze direction in the environment. For half the trials, blur foils were used to restrict visual acuity to approximately logMAR 1.65. Gaze behavior, travel time, and letter recognition accuracy were compared between blurred and unrestricted conditions. In the second experiment, the same procedure was conducted, but performance was compared between acuity-restricted normally-sighted subjects and subjects with naturally occurring low vision (mean acuity 1.09 logMAR, range 0.48-1.85 logMAR). In Experiment 1, neither Blur nor the Letter Recognition Task individually had a statistically significant effect on travel time. However, when combined, there was an interaction between the two that increased travel time by approximately 63%, relative to baseline trials. Blur modified gaze behavior such that subjects spent more time looking down toward the floor while walking, at the expense of time spent looking in other directions. During Letter Recognition Task trials with Blur, subjects spent extra time examining objects, though more objects were missed altogether. In Experiment 2, low-vision subjects spent more time looking toward the boundary between the floor and the wall, but gaze patterns were otherwise similar to acuity-restricted subjects with normal vision. Low-vision subjects were also more likely to miss objects compared to acuity-restricted subjects. We conclude that under conditions of artificially restricted acuity, normally sighted subjects look downward toward the floor more frequently while navigating and take extra time to examine objects of interest, but are less likely to detect them. Low-vision subjects tend to direct their gaze toward the boundary between the wall and the floor, which may serve as a high contrast cue for navigation.