The role of binocular vision in walking

Abstract

Despite the extensive investigation of binocular and stereoscopic vision, relatively little is known about its importance in natural visually guided behavior. In this paper, we explored the role of binocular vision when walking over and around obstacles. We monitored eye position during the task as an indicator of the difference between monocular and binocular performances. We found that binocular vision clearly facilitates walking performance. Walkers were slowed by about 10% in monocular vision and raised their foot higher when stepping over obstacles. Although the location and sequence of the fixations did not change in monocular vision, the timing of the fixations relative to the actions was different. Subjects spent proportionately more time fixating the obstacles and fixated longer while guiding foot placement near an obstacle. The data are consistent with greater uncertainty in monocular vision, leading to a greater reliance on feedback in the control of the movements.

Fig. 1

(Color online) The walking path. (a) Subjects started at the left near the wall, stepped over the two boxes, walked on the right side of the table, then between table and wall, and stepped over the boxes again on the return path to the starting point. (b) The height of the obstacles and table.

Fig. 2

(a) (Color online) RIT wearable tracker. (b) Illustration of the point at which toe clearance was measured (see text).

Fig. 3

Time to walk over the boxes and around the table for the monocular (left) and binocular (right) conditions. The total time is the sum of the two components. Error bars are S.E.M. between subjects. N = 26.

Fig. 4

Mean height clearance for the foot above the top of the box as it passes over the box for monocular (left) and binocular (right) conditions. Data are averaged for the two boxes, for front and back edges, and for both directions of walking. Error bars are ±1 S.E.M. between subjects. N = 26.

Fig. 5

Proportion of time fixating the obstacles and the path for monocular (left) and binocular (right) conditions. Error bars are ±1 S.E.M. between subjects. N = 8.

Fig. 6

Total time fixating the boxes and the table for monocular (left) and binocular (right) conditions. Error bars are ±1 S.E.M. between subjects. N = 8.

Fig. 7

Scatter plots of fixations on box 2 and on the table. Monocular condition is blue, and binocular is red. Fixations for eight subjects are shown.

Fig. 8

(Color online) Illustration of the difference in foot guidance while stepping over the box, for binocular (left) and monocular (right) conditions. Fixation position is indicated by a red cross for three successive times. The blue outline indicates the foot/leg within some frames. Binocular condition images cover 233 ms, and monocular condition images cover 300-ms time period.

Fig. 9

Average foot guidance times for monocular, for binocular and monocular conditions. Error bars are ±1 S.E.M. between subjects, N = 8.

Fig. 10

(A) Average fixation durations on box 2 as a function of trial number, for binocular and monocular conditions. Monocular is shown in light gray and binocular in dark gray. Dashed lines connect trials performed by the same group (MBBM for one group and BMMB for the other). (B) Average fixation durations during foot guidance, as a function of trial number. (C) Total trial duration as a function of trial number. Error bars are ±1 S.E.M. between subjects.