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. Author manuscript; available in PMC: 2012 Oct 1.
Published in final edited form as: J Exp Psychol Hum Percept Perform. 2011 Oct;37(5):1442–1457. doi: 10.1037/a0023510

Figure 1.

Figure 1

Top down view of an observer (width W) moving along a straight path, with two obstacles (diameter D) converging on a point along the observer’s future path. θ is the visual direction of the obstacle relative to the direction of locomotion and φ is the visual angle subtended by the obstacle. The distance along the frontal plane from the observer to the obstacles at the moment that the obstacles pass by the observer is the future lateral passing distance. In this example, the future lateral passing distance is greater than [½(W+D)], indicating that the observer will safely pass through the gap if current speed is maintained.