View rotation is used to perceive path curvature from optic flow.

In many natural situations like driving a car, path curvature is accompanied by observer rotation. The experiments reported here test whether such view rotation is necessary to perceive path curvature from optic flow. Displays simulated travel on a circular path along a random dot ground plane, with speeds of 4 m/s and curvature of ±2°/s. In the Rotating View condition, the view direction rotated with heading, as in previous studies. In the Non-rotating View condition, displays simulated travel along the same circular paths but without change in view direction. In Experiment 1, observers indicated positions on their perceived future path at various distances. Judgments were consistent with curved paths in the Rotating View condition, while in the Non-rotating View condition, judgments were consistent with straight paths. In Experiment 2, observers reported whether the simulated path was straight, curved leftward, or curved rightward. Judgments were accurate in the Rotating View condition, while in the Non-rotating View condition, curved paths were often reported to be straight, and observers did not reliably distinguish the sign of curvature. In both experiments, observers had difficulty perceiving path curvature from optic flow when it was not accompanied by view rotation.