Rotation is used to perceive path curvature from optic flow

Abstract

Previous studies have found that observers can reliably judge their future trajectory along a circular path from optic flow. However, observers have difficulty distinguishing straight and circular paths in some conditions, suggesting insensitivity to optical acceleration. How are observers able to account for path curvature when judging a future circular path? One explanation is that instantaneous rotation is used as a cue for curvature. In many situations, such as driving, the body rotates in sync with change in heading direction, so rotation provides a reliable cue. The purpose of this study was to test whether the visual system relies on rotation to perceive path curvature from optic flow. Stimuli simulated travel along a circular path on a random dot ground plane, with speeds of 2 m/s and curvature (yaw) of 2°/s. Two conditions differed in simulated view rotation. In the rotating view condition, view direction rotated in sync with heading direction, as in previous studies. In the fixed view condition, displays simulated travel along the same circular paths but without change in view direction. In Experiment 1, observers indicated their perceived future path at various distances by adjusting the horizontal position of a pole. Judgments were consistent with curved paths in the rotating view condition, while in the fixed view condition, judgments were consistent with straight paths. In Experiment 2, observers reported whether their perceived path was straight, curved leftward, or curved rightward. Judgments were highly accurate in the rotating view condition, while in the fixed 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, consistent with use of rotation as a perceptual cue to curvature. © 2010 ARVO