Perception of Tilt and Ocular Torsion of Normal Human Subjects During Eccentric Rotation

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Abstract
Hypothesis The authors hypothesized that a nonvisual measure of the subjective horizontal during eccentric rotation is a reliable method for evaluating the spatial orientation of normal subjects during such rotation. Background Eccentric rotation is a promising tool for the evaluation of otolithic function in healthy subjects and in patients. Although eye torsion is an objective measurement, it is also affected by angular acceleration/deceleration. Subjective horizontal is more accurately related to the changes in linear acceleration, but visual judgments of orientation are confounded by ocular torsion. Methods 20 subjects were tested during eccentric yaw rotation in both directions, generating centripetal acceleration directed along the interaural axis ranging from 0.38 g to 1 g. Perception of body tilt in roll and in pitch was recorded in darkness using verbal reports and a somatosensory plate that the subjects maintained parallel to the perceived horizon. Torsion of the eyes was recorded by a video camera. Results Perceived roll tilt was close to the tilt of the gravito-inertial acceleration vector. However, there were differences in perceived roll and pitch tilt between facing-motion and back-to-motion headings, presumably related to the direction of the tangential acceleration. Ocular torsion was dependent on both angular and centripetal accelerations. Conclusions Measurement of perceived roll and pitch tilt using a somatosensory plate is a reproducible method for quantifying the effects of linear accelerations during eccentric rotation. This method may prove useful for the diagnosis of otolithic dysfunction in dizziness and in patients with vestibular disorders.