Eye-position dependence of torsional velocity during step-ramp pursuit and transient yaw rotation in humans.
The time course of eye-position-dependent torsion during transient horizontal pursuit and yaw rotation was examined in seven normal human subjects. The stimuli consisted of step-ramp target motion (25, 40 degrees /s) and brief chair rotation (approximately 200 degrees /s(2) accelerated to 40 degrees /s) at three different vertical positions (center 0 degrees , up or down 15 degrees ). Three-dimensional eye movements were recorded with dual search coils. The kinematics of pursuit and the rotational vestibulo-ocular reflex (rVOR) were assessed by determining the tilt-angle slope, a measure of the variation of the axis of eye-velocity with vertical eye position. We found that the tilt-angle slope during pursuit was initially 0.4+/-0.07 (mean+/-95% confidence interval) and then gradually rose to 0.64+/-0.04, at about the time that the steady-state eye-velocity was reached. The rVOR began with a nearly head-fixed axis (0.08+/-0.04), appropriate for full retinal image stabilization, followed by a gradual increase of the tilt-angle slope to 0.31+/-0.02. Thus, differences between pursuit and the rVOR with respect to Listing's law can be seen from the onset of transient responses, although in both cases eye-position-dependent torsion increases with time. This temporal evolution of the axis of eye-velocity may involve the velocity-storage mechanism.
Tian
Jing
J
Department of Neurology, The Johns Hopkins University School of Medicine, 600 N. Wolfe Street, Pathology 2-210, Baltimore, MD, 21287, USA.
Zee
David S
DS
Walker
Mark F
MF
D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D005123:Eye; D006801:Humans; D008875:Middle Aged; D011698:Pursuit, Smooth / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012399:Rotation; D013997:Time Factors; D014102:Torsion Abnormality / Q000503:physiopathology*