Perception of passage through openings depends on the size of the body in motion

Abstract

Walkers need to modify their ongoing actions to meet the demands of everyday environments. Navigating through openings requires gait modifications if the size of the opening is too small relative to the body. Here we ask whether the spatial requirements for navigating horizontal and vertical openings differ, and, if so, whether walkers are sensitive to those requirements. To test walkers' sensitivity to demands for gait modification, we asked participants to judge whether they could walk through horizontal openings without shoulder rotation and through vertical openings without ducking. Afterward, participants walked through the openings, so that we could determine which opening sizes elicited gait modifications. Participants turned their shoulders with more space available than the space they left themselves for ducking. Larger buffers for horizontal openings may reflect different spatial requirements created by lateral sway of the body during walking compared to vertical bounce. In addition, greater variability of turning from trial to trial compared with ducking may lead walkers to adopt a more conservative buffer to avoid errors. Verbal judgments accurately predicted whether openings required gait modifications. For horizontal openings, participants' judgments were best predicted by the body's dynamic abilities, not static shoulder width. The differences between horizontal and vertical openings illustrate that walkers account for the dynamic properties of walking in addition to scaling decisions to body dimensions.

Fig 1

Adjustable opening apparatus presented horizontal and vertical openings that elicit gait modifications: (a) horizontal openings were adjusted by moving a sliding wall and (b) vertical openings were adjusted by moving a screen. Arrows indicate the direction of the adjustment for each condition.

Fig 2

Scatter plots showing correlations between thresholds and relevant body dimensions in the verbal judgment and walking tasks. Top row: shoulder-width scaling of judged turning thresholds left) and actual turning thresholds (right). Bottom row: height scaling of judged ducking thresholds (left) and actual ducking thresholds (right).

Fig 3

Means and standard errors of (a) turning and ducking ratios, (b) turning and ducking buffers, and (c) response variability. Grey bars indicate values for actual gait modifications and white bars show verbal judgments. Ratios greater than 1 and buffers greater than 0 (horizontal reference lines) indicate that participants left space in addition to their shoulder width and height.