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L. H. Yoo, B. T. Crane, J.-R. Tian, J. L. Demer; Human, Whole-Body Rotational Stimulator of Torsional and Vertical Vestibulo-Ocular Reflex (VOR). Invest. Ophthalmol. Vis. Sci. 2007;48(13):893.
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© ARVO (1962-2015); The Authors (2016-present)
Earth-horizontal axis (EHA) rotation may include pitch, roll, or combinations of these motions that stimulate both the otoliths and semicircular canals (SCCs). The human VOR during EHA rotation remains enigmatic, largely due to the difficulty of delivering controlled vestibular stimuli during eye movement recording. We developed a whole-body EHA rotator capable of delivering high accelerations about controlled EHA axes, while compatible with 3-D recording of eye and head motion.
Within a large stationary 3-frequency sinusoidal magnetic field generator, we constructed a rotator framework of non-magnetic materials. Rotator half axles were milled from PVC pipe, and passed through bearings made of Mb-impregnated nylon. Both half axles were driven by digitally synchronized, stepper motors with total torque 1 N-km(740ft-lb). The subject chair was placed so that the rotational axis passed through, or at a specified eccentricity from, the labyrinths. Stresses in structural components were analyzed analytically and by finite element analysis; using Rankine’s criterion, the safety factor for each part was ≥3.1. Chair and head motion were evaluated using magnetic search coils and linear accelerometers.
The rotator achieved well-coupled, whole-body rotations of 12 adults about pitch, roll, and intermediate axes passing through the labyrinths. Peak sinusoidal and random transient rotations, recorded at the skull, were highly repeatable ≤2,000°/s2, ≤300°/s, and ≤50°. Subjects reported satisfactory comfort during both transient rotations and sustained tilts ≤45°. Rotator operation was magnetically compatible with low noise, 3-D search coil recording, and with simultaneous presentation of visual stimuli 30 - 300 cm away.
A rotator is now available for detailed study of human VORs during EHA rotation about axes at or near the vestibular labyrinths. EHA acceleration is sufficient for robust determination of temporal dynamics of human SCC and otolith-evoked VORs, and to induce inhibitory cutoff in individual SCC afferents.
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