Humans can use optic flow to estimate distance of travel

We demonstrate that humans can use optic flow to estimate distance travelle d when appropriate scaling information is provided. Eleven subjects were pr esented with visual targets in a virtual corridor. They were then provided with optic flow compatible with movement along the corridor and asked to in dicate when they had reached the previously presented target position. Perf ormance depended on the movement profile: for accelerations above 0.1 m/s(2 ) performance was accurate. Slower optic-how acceleration resulted in an ov erestimation of motion which was most pronounced for constant velocity moti on when the overestimation reached 170%. The results are discussed in terms of the usual synergy between multiple sensory cues to motion and the facto rs that might contribute to such a pronounced miscalibration between optic flow and the resulting perception of motion. (C) 2001 Elsevier Science Ltd. All rights reserved.