title: Gain of human torsional optokinetic nystagmus depends on horizontal disparity.
abstract: OBJECTIVE
  To investigate the effects of horizontal disparity on torsional optokinetic nystagmus (tOKN) in humans.
  
  
  METHODS
  Ten healthy human subjects were selected for this experiment. Monocular eye movements were recorded three-dimensionally using dual-search coil methods. Torsional OKN was induced by a rotating random-dot pattern (22 degrees in diameter, constant angular velocity: +/-54 deg/s) projected on the virtual screen of the optical see-through, head-mounted display (HMD). The optical distance of the HMD's virtual screen was 2 m. A red LED that could be fixated through the virtual screen of the HMD was located near the center of the rotating random-dot pattern. Horizontal disparity was induced by changing the distance between the fixated target and the subject systematically (1, 1.5, 2, or 3 m; five subjects) or by the prism (+1.5, +0.5, 0, or -0.5 prism-diopter [PD] in each eye; five subjects) in front of the HMD.
  
  
  RESULTS
  The average gain with zero horizontal disparity (0.022 +/- 0.008/0.025 +/- 0.014, fixated target at 2 m/fixated target with the plain glass) was significantly higher than the gain with crossed disparity (0.017 +/- 0.003/0.019 +/- 0.008, target at 3 m/with the prism of -0.5 PD) and uncrossed disparity (0.017 +/- 0.002, target at 1 m/with the prism of +1.5 PD; one-way ANOVA, P <0.05).
  
  
  CONCLUSIONS
  The horizontal disparity of optokinetic stimulus affects tOKN. Nonzero horizontal disparity decreases the gain of tOKN.
authors.affiliation: Department of Ophthalmology, Sapporo Medical University, School of Medicine, Sapporo, Japan.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Washio
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sawa
authors.forename: Kenji
authors.initials: K
authors.lastname: Ohtsuka
mesh_terms: D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D014102:Torsion Abnormality; D015357:Vision Disparity / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology