Figure 3.

Optically specified distance (A), time remaining (B), and speed (C,D) to pass in front (red line) and behind (blue line) for a stationary observer and a moving obstacle, similar to the situation depicted in Figure 2A. (A–C) Are for a small obstacle, and (D) is for a larger obstacle. Values were calculated using optical variables in Equations 7 and 8. E is the observer's eyeheight, s is seconds, and V_max is the observer's maximum locomotor speed. Gray area in (C) and (D) indicate range of speeds that would result in a collision.