P‐12: The Effects of Simulated Texture Flow Rates on Estimates of Time‐to‐Collision

The ratio (τ) of a 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 texture flow rates (i.e., optical flow rates), consistent with simulated observer motion, affect judgments of time-to-collision (TTC). TTC was estimated for various relative velocities of the observer and a circular target. Relative velocity was varied such that the proportion of the total closing velocity attributable to the observer was either 0.0, 0.33, 0.67, or 1.0. Since the closing velocity between the observer and target was held constant, visual information for τ was the same under all test conditions. However, visual information (i.e., texture flow rate) for simulated self-motion was varied. The Weber fraction for estimated TTC progressively decreased as the proportion of observer motion increased, indicating that estimated TTC decreased as texture flow rate increased. This result has practical implications for judging TTC in high-fidelity flight simulators, since the rendering of terrain texture detail directly affects both texture flow rates and the perception of self-motion, either of which may effect estimated TTC.