Tests of a linear model of visual-vestibular interaction using the technique of parameter estimation |
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Authors: | Vallabh E Das Alfred O DiScenna Andrew Feltz Stacy Yaniglos R John Leigh |
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Institution: | (1) Department of Neurology, Department of Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio, USA, US;(2) Department of Biomedical Engineering, Department of Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio, USA, US;(3) Department of Optometry, Department of Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio, USA, US;(4) Department of Neuroscience, Department of Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, Ohio, USA, US |
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Abstract: | The goal of this study was to test whether a superposition model of smooth-pursuit and vestibulo-ocular reflex (VOR) eye
movements could account for the stability of gaze that subjects show as they view a stationary target, during head rotations
at frequencies that correspond to natural movements. Horizontal smooth-pursuit and the VOR were tested using sinusoidal stimuli
with frequencies in the range 1.0–3.5 Hz. During head rotation, subjects viewed a stationary target either directly or through
an optical device that required eye movements to be approximately twice the amplitude of head movements in order to maintain
foveal vision of the target. The gain of compensatory eye movements during viewing through the optical device was generally
greater than during direct viewing or during attempted fixation of the remembered target location in darkness. This suggests
that visual factors influence the response, even at high frequencies of head rotation. During viewing through the optical
device, the gain of compensatory eye movements declined as a function of the frequency of head rotation (P < 0.001) but, at any particular frequency, there was no correlation with peak head velocity (P > 0.23), peak head acceleration (P > 0.22) or retinal slip speed (P > 0.22). The optimal values of parameters of smooth-pursuit and VOR components of a simple superposition model were estimated
in the frequency domain, using the measured responses during head rotation, as each subject viewed the stationary target through
the optical device. We then compared the model's prediction of smooth-pursuit gain and phase, at each frequency, with values
obtained experimentally. Each subject's pursuit showed lower gain and greater phase lag than the model predicted. Smooth-pursuit
performance did not improve significantly if the moving target was a 10 deg × 10 deg Amsler grid, or if sinusoidal oscillation
of the target was superimposed on ramp motion. Further, subjects were still able to modulate the gain of compensatory eye
movements during pseudo-random head perturbations, making improved predictor performance during visual-vestibular interactions
unlikely. We conclude that the increase in gain of eye movements that compensate for head rotations when subjects view, rather
than imagine, a stationary target cannot be adequately explained by superposition of VOR and smooth-pursuit signals. Instead,
vision may affect VOR performance by determining the context of the behavior.
Received: 16 June 1997 / Accepted: 5 December 1997 |
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