title: Pitch body orientation influences the perception of self-motion direction induced by optic flow.
abstract: We studied the effect of static pitch body tilts on the perception of self-motion direction induced by a visual stimulus. Subjects were seated in front of a screen on which was projected a 3D cluster of moving dots visually simulating a forward motion of the observer with upward or downward directional biases (relative to a true earth horizontal direction). The subjects were tilted at various angles relative to gravity and were asked to estimate the direction of the perceived motion (nose-up, as during take-off or nose-down, as during landing). The data showed that body orientation proportionally affected the amount of error in the reported perceived direction (by 40% of body tilt magnitude in a range of +/-20 degrees) and these errors were systematically recorded in the direction of body tilt. As a consequence, a same visual stimulus was differently interpreted depending on body orientation. While the subjects were required to perform the task in a geocentric reference frame (i.e., relative to a gravity-related direction), they were obviously influenced by egocentric references. These results suggest that the perception of self-motion is not elaborated within an exclusive reference frame (either egocentric or geocentric) but rather results from the combined influence of both.
authors.affiliation: UMR CNRS 6233, Institut des Sciences du Mouvement Etienne-Jules Marey, CNRS & Aix-Marseille Université, 163, avenue de Luminy, CP 910, 13288 Marseille, France. aurore.bourrelly@hotmail.fr
authors.forename: A
authors.initials: A
authors.lastname: Bourrelly
authors.forename: J-L
authors.initials: JL
authors.lastname: Vercher
authors.forename: L
authors.initials: L
authors.lastname: Bringoux
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007699:Kinesthesis / Q000502:physiology*; D008297:Male; D010465:Perception / Q000502:physiology*; D010775:Photic Stimulation; D011187:Posture / Q000502:physiology*