title: Postural adjustment response to depth direction moving patterns produced by virtual reality graphics.
abstract: OBJECTIVE
  Human posture is controlled by a combination of vestibular, somatosensory and visual information. This paper is concerned with postural readjustment responses induced by vection. In the visual control of posture, visually-induced perception of self-motion plays an important role and is called vection. Vection is difficult to measure quantitatively because it is a highly subjective phenomenon.
  
  
  OBJECTIVE
  An optokinetic stimulus that moves in depth induces vection. We hypothesize that the magnitude of the visually-induced body sway is correlated with the degree of vection.
  
  
  METHODS
  A depth optokinetic stimulus (DOKS) was projected onto a head-mounted display (HMD) worn by standing subjects. The DOKS consisted of a random dot pattern that was perceived three-dimensionally and moved in depth sinusoidally. Vection was estimated in two ways, a verbal assessment and a joystick maneuver. In addition, visually-induced body sway was measured by monitoring five reference points on the body by two video-motion analyzers.
  
  
  RESULTS
  The magnitude of the subjective vection was highly correlated with visually-induced body sway and was strongly dependent on the velocity of the visual stimulus. The ankle joint was pivoted during visually-induced body sway and acted as a motion initiator. When the magnitude of body sway was large, the body movement was adjusted at the hip and head-neck joints.
  
  
  CONCLUSIONS
  The high correlation between vection and body sway suggests that vection can be estimated quantitatively by measuring visually-induced body sway.
authors.affiliation: Department of ophthalmology, Nagoya University School of Medicine, Showa-ku, Nagoya, 466-0065, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kuno
authors.forename: T
authors.initials: T
authors.lastname: Kawakita
authors.forename: O
authors.initials: O
authors.lastname: Kawakami
authors.forename: Y
authors.initials: Y
authors.lastname: Miyake
authors.forename: S
authors.initials: S
authors.lastname: Watanabe
mesh_terms: D000328:Adult; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006257:Head; D006801:Humans; D008297:Male; D008606:Mental Processes / Q000502:physiology; D009039:Motion Perception / Q000502:physiology*; D010775:Photic Stimulation; D011187:Posture / Q000502:physiology*; D011340:Problem Solving / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D014584:User-Computer Interface; D014741:Video Recording