A veridical percept of ego-motion is normally derived from a combination of visual, vestibular, and proprioceptive signals. In a previous study,
blindfolded subjects could accurately perceive passively travelled straight or curved trajectories provided that the orientation of the head
remained constant along the trajectory. When they were turned (whole-body, head-fixed) relative to the trajectory, errors occurred. We ask here
whether vision allows for better path perception in similar tasks, to correct or complement vestibular perception. Seated, stationary subjects wore
a head mounted display showing optic flow stimuli which simulated linear or curvilinear 2D trajectories over a horizontal ground plane. The
observer's orientation was either fixed in space, fixed relative to the path, or changed relative to both. After presentation, subjects reproduced the
perceived movement with a model vehicle, of which position and orientation were recorded. They tended to correctly perceive ego-rotation
(yaw), but they perceived orientation as fixed relative to trajectory or (unlike in the vestibular study) to space. This caused trajectory
misperception when body rotation was wrongly attributed to a rotation of the path. Visual perception was very similar to vestibular perception