World-centered perception of 3D object motion during visually guided self-motion.

We investigated how human observers estimate an object's three-dimensional (3D) motion trajectory during visually guided self-motion. Observers performed a task in an immersive virtual reality system consisting of front, left, right, and floor screens of a room-sized cube. In one experiment, we found that the presence of an optic flow simulating forward self-motion in the background induces a world-centered frame of reference, instead of an observer-centered frame of reference, for the perceived rotation of a 3D surface from motion. In another experiment, we found that the perceived direction of 3D object motion is biased toward a world-centered frame of reference when an optic flow pattern is presented in the background. In a third experiment, we confirmed that the effect of the optic flow pattern on the perceived direction of 3D object motion was not caused only by local motion detectors responsible for the change of the retinal size of the target. These results suggest that visually guided self-motion from optic flow induces world-centered criteria for estimates of 3D object motion.