Perceiving path from optic flow.

We examined how people perceive their path of traveling from optic flow. Observers viewed displays simulating their traveling on a circular path over a textured ground, a random-dot ground, or a dynamic random-dot ground display in which dots were periodically redrawn to remove extended dot motion trajectories (flow lines) in the flow field. Five viewing conditions were tested in which the simulated observer gaze direction was pointed to (1) a target on the path at 30° away from the initial heading, (2) a target at 15° outside of the path, (3) a target at 15° inside of the path, (4) along the instantaneous heading, or (5) along the Z-axis of the simulated environment. Path performance was similar for all three display conditions, indicating that observers did not rely on flow lines to perceive path from optic flow. Furthermore, contrary to the idea that looking where you want to go provides accurate path perception, path perception was accurate only when the simulated observer gaze direction pointed in the instantaneous heading direction. In contrast, heading perception was accurate and not affected by path curvature regardless of the simulated gaze direction. The results suggest that heading perception is more robust than path perception.