The effect of viewing location and direction of gaze in determining whether a gap is crossable
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The basic environmental constraint on whether a gap is crossable is its width, i.e., the distance between the edges of two surfaces of support. The gap's depth does not affect a person's capability. However, previous work (Jiang, 1991) has shown that when observers are asked to estimate the maximum gap width they can step across, judgments covary as a function of gap depth-that is, as gap depth increases, observers increasingly underestimate their actual capabilities. A follow-up study (Jiang & Mark, 1992) clarified Jiang's initial finding by showing that estimates of gap crossing capabilities depended crucially on where observers directed their gaze; when looking down into the gap, observers tended to underestimate their capabilities more than when they looked toward the horizon.