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The Journal of Neurophysiology Vol. 86 No. 5 November 2001, pp. 2323-2329
Copyright ©2001 by the American Physiological Society
1Department of Neurology, 2Department of Biomedical Engineering, and 3Department of Neurosciences, Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio 44106
Han, Yanning,
Jeffrey T. Somers,
Jae I. Kim,
Arun N. Kumar, and
R. John Leigh.
Ocular Responses to Head Rotations During Mirror Viewing. J. Neurophysiol. 86: 2323-2329, 2001. The
gain of the human vestibuloocular reflex (VOR) is influenced by the
proximity of the object of regard. In six human subjects, we measured
the eye rotations induced by passive, sinusoidal, horizontal head
rotations at 2.0 Hz during binocular fixation of a stationary far
target at 7 m; a stationary target close to the subject's near
point of fixation (<15 cm); and the bridge of the subject's own nose,
viewed through a mirror positioned so that, for each subject, the angle
of vergence was similar to that during viewing of the near target. The
median gain of compensatory eye movements for the group of subjects
during far viewing was 0.99 (range 0.80-1.04), during near viewing was
1.21 (range 0.88-1.47), and during mirror viewing was 0.85 (range
0.71-1.01). The gain during near and mirror viewing was significantly
different for each subject (P < 0.001) even though the
vergence angles were similar. The lower gain values during mirror
viewing can be attributed to the geometric relationship between the
head rotation, the position of the eyes in the head, and the movement
of the subject's virtual image in the mirror. To determine whether
visually mediated eye movements were responsible for the observed gain
values, we conducted a control experiment in which subjects were
rotated using a sum-of-sines stimulus that minimized the effects of
predictive visual tracking; differences of gain values between near-
and mirror-viewing conditions were similar to those during rotation at
2 Hz. We conclude that, in these experiments, target proximity and
vergence angle were not the key determinants of gain of the
visuo-vestibular response during head rotation while viewing a near
target but that contextual cues from motion vision were more important
in generating the appropriate response.
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