title: The human vertical optokinetic afternystagmus and the effect of gravity during pitch tilt.
abstract: BACKGROUND
  Findings concerning human vertical optokinetic afternystagmus (VOKAN) are often not consistent and in some cases even contradictory.
  
  
  METHODS
  VOKAN was studied in nine normal subjects using corneo-retinal potential technique and an infrared video camera detection apparatus (ISCAN). VOKAN responses were measured at three angles of pitch head (and body) tilt: 0 degrees (upright), 90 degrees (supine) and 135 degrees (45 degrees below horizontal). The optokinetic stimulus was stripe movement with a velocity of 60 degrees/s.
  
  
  RESULTS
  Upward slow phase velocity (SP-Up) VOKAN was evoked in 6/9 subjects (67%) at 0 degrees tilt and at 90 degrees tilt, and in 4/9 (44%) at 135 degrees tilt. Downward slow phase velocity (SP-Down) VOKAN was elicited in 3/9 subjects (33%) at 0 degrees tilt; in 2/9 subjects (22%) at 90 degrees tilt and in 0/9 subjects (0%) at 135 degrees tilt.
  
  
  CONCLUSIONS
  The pitch tilt, as a gravity effect, influences significantly on the appearance and the duration of VOKAN.
authors.affiliation: The Naval Aerospace Medical Research Laboratory, Pensacola, FL, USA. stayko.kolev@meteo.bg
authors.forename: O I
authors.initials: OI
authors.lastname: Kolev
authors.forename: A H
authors.initials: AH
authors.lastname: Rupert
mesh_terms: D000328:Adult; D005133:Eye Movements / Q000502:physiology; D006112:Gravitation; D006801:Humans; D007259:Infrared Rays; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D014743:Videotape Recording