Pictorial and motion-based depth information during active control of self-motion: size-arrival effects on collision avoidance.

With computer simulations of self-motion, Ss controlled their altitude as they approached a floating object and, after getting as close as possible to the object, tried to "jump" over it without collision. Ss jumped significantly later for small objects, compared with larger objects that were approached from equal distances at equal speeds and were positioned at equal clearance heights. This occurred even when accretion-deletion information was present and when object width and length were varied independently. Results were consistent with studies in which Ss judged a large far approaching object to hit the viewpoint before a small near object that would have arrived sooner (P.R. DeLucia, 1991a, 1991b). Results suggest that pictorial information such as relative size contributes to active collision-avoidance tasks and must be considered in models of perceived distance and time-to-arrival.