Linear acceleration and horizontal eye movements in man.

Abstract

Horizontal eye movements in humans were studied under several stimulus conditions: 1) Linear vestibulo-ocular reflex (LVOR) during lateral accelerations in the dark; 2) Tracking of a retinally-fixed after-image (AI) during identical accelerations; 3) Fixation suppression (FS) of LVOR by fixating on a subject-stationary target light during linear acceleration; 4) Smooth pursuit (SP) in response to a moving visual target; 5) Tracking a stationary target while undergoing linear accelerations, providing both visual and vestibular information (VV). The last condition determined the improvement in smooth pursuit due to additional vestibular sensory input. Subject and target motions were sinusoids of various frequencies and peak accelerations, acceleration steps, and pseudo-random sum-of-sinusoids. Frequency response functions were produced from gain and phase measurements of the eye motion with respect to the target/subject motion. Fast phases were removed from eye movement records via computer processing. Results confirm that LVOR is highly variable, with a gain of about fifteen degrees per second of eye movement per g of acceleration, relatively constant across the frequency range 0.2 to 1.3 Hz. AI tracking improves the gain of the LVOR by a factor of two to ten. This provides support for a theory in which oculomotor efferent copy information is used to reconstruct an internal representation of target velocity, which is then tracked by the oculomotor system. Fixation suppression significantly reduces the LVOR gain. Comparison of the VV and SP conditions shows that the additional linear motion information provided by accelerating the subject in the VV condition produces a small but significant improvement in oculomotor tracking. This improvement is manifest most consistently by a decrease in phase lag, and also by an increase in response gain (eye movement divided by target movement). A Kalman filter-based model of the combination of visual and vestibular information for oculomotor tracking is developed. The model concentrates on predictable (sinusoidal) target motion, and contains a central pattern generator (CPG) which predicts the target motion and hence enhances the response. The CPG is a natural formulation of the Kalman filter when the input is known to be sinusoidal. The CPG requires an instantaneous estimate of the input frequency, provided by a frequency estimator subsystem derived from a linearized Kalman filter. The model performance is compared to the experimental data. (AUNT Concern for man, himself, and his fate must always form the chief interest of all technical endeavor...Never forget this in the midst of your diagrams and equations.-Albert …

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@article{Shelhamer1991LinearAA, title={Linear acceleration and horizontal eye movements in man.}, author={Mark Shelhamer and Laurence R. Young}, journal={Acta oto-laryngologica. Supplementum}, year={1991}, volume={481}, pages={277-81} }