Time-To-Contact Estimates for Observer versus Target Motion

Abstract

The ratio (τ) of a moving target's angular size to the rate of change in its angular size can be used by observers to judge the time remaining before they will collide with the target. We consider here whether optical flow information, consistent with simulated observer motion, affects observers' estimates of time-to-contact (TTC). Estimates of TTC were obtained when either the observer approached a stationary target or the target approached a stationary observer. The visual information for τ was the same in both conditions, whereas the visual information for observer self-motion was varied. For the low closing velocities, (3 and 6 eyeheights/sec) there was no significant difference in the estimated TTC for observer motion versus target motion. However, there was a significant difference for the highest closing velocity (12 eyeheights/sec). This result suggests that visual information, specifying self-motion, may be used either in combination with or in place of τ to estimate TTC during simulated locomotion. The present findings have practical implications for both the use of τ in judging TTC and the rendering of terrain texture detail in high-fidelity flight simulators.