Perception threshold for tilt.

The aim of this study was to determine the thresholds for perception of tilt and translation using 3 motion/tilt profile paradigms. Healthy subjects were submitted to the following: 1) unilateral and bilateral eccentric rotations (centrifugation), 2) whole body translatory decelerations opposite to the movement direction while seated on a linear sled, and 3) discrete slow velocity platform tilts. Subjects were instructed to verbally indicate the perceived direction of tilt or translation. Fifteen healthy subjects (12 male and 3 female subjects, 18-31 yr) without any history or evidence of any ophthalmologic or neuro-otologic disorder participated in this study. Our results from unilateral centrifugation indicate a threshold for body tilt perception of approximately 2 degrees with a substantial interindividual range (1.9-5.6 degrees, 52% interindividual and 34% intraindividual variability), which, to our interpretation, mainly depends on otolithic function. Tilt perception during whole body decelerations and discrete platform tilts mainly depends on somatosensory information, showing the dominant role of the somatosensory system for the perception of body orientation. Thus, tilt sensations during eccentric rotations seems to be a promising tool for the evaluation of utricular dysfunction.