title: Kinematics of vertical saccades during the yaw vestibulo-ocular reflex in humans.
abstract: OBJECTIVE
  Listing's law (LL) constrains the rotational axes of saccades and pursuit eye movements to Listing's plane (LP). In the velocity domain, LL is ordinarily equivalent to a tilt in the ocular velocity axis equal to half the change in eye position, giving a tilt angle ratio (TAR) of 0.5. This study was undertaken to investigate vertical saccade behavior after the yaw vestibulo-ocular reflex (VOR) had driven eye torsion out of LP, an initial condition causing the position and velocity domain formulations of LL to differ.
  
  
  METHODS
  Binocular eye and head motions were recorded with magnetic search coils in eight humans. With the head immobile, LP was determined for each eye, and mean TAR was 0.50 +/- 0.07 (mean +/- SD) for horizontal and 0.45 +/- 0.11 for vertical saccades. The VOR was evoked by transient, whole-body yaw at 2800 deg/s2 peak acceleration, capable of evoking large, uninterrupted VOR slow phases. Before rotation, subjects viewed a target at eye level, 20 degrees up, or 20 degrees down. In two thirds of the trials, the target moved upward or downward at systematically varying times, triggering a vertical saccade during the horizontal VOR slow phase.
  
  
  RESULTS
  Because the head rotation axis was generally misaligned with LP, the eye averaged 3.6 degrees out of LP at vertical saccade onset. During the saccade, eye position continued to depart LP by an average 0.8 degrees. The horizontal TAR at saccade onset was 0.29 +/- 0.07. At peak saccade velocity 35 +/- 3 ms later, the vertical TAR was 0.45 +/- 0.07, statistically similar to that of head fixed saccades. Saccades did not return to LP.
  
  
  CONCLUSIONS
  Although they did not observe the position domain formulation of LL, vertical saccades, during the VOR, observed the half-angle velocity domain formulation of LL.
authors.affiliation: Department of Surgery (Division of Otolaryngology), University of California, Los Angeles, CA 90095-7002, USA.
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Crane
authors.forename: Junru
authors.initials: J
authors.lastname: Tian
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004574:Electromagnetic Fields; D005260:Female; D019416:Head Movements / Q000502:physiology; D006801:Humans; D008297:Male; D009799:Ocular Physiological Phenomena; D011187:Posture; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012399:Rotation; D012438:Saccades / Q000502:physiology*