Thresholds for Human Perception of Roll Tilt Motion: Patterns of Variability Based on Visual, Vestibular, and Mixed Cues

Hypothesis: Visual and vestibular cues provide complementary information about spatial orientation. Background: A previous study we performed showed that visual and vestibular cues are fused when the brain judges the roll-tilt direction. However, it was unclear if the motion perception threshold measured in visual-vestibular conditions will be better than visual or vestibular thresholds at high frequencies. Methods: An innovative method of vestibular evaluation, the measurement of vestibular thresholds, was used. We used a Moog mobile platform with dedicated software. Four subjects were tested at 1, 2, 3, 4, and 5 Hz with adaptively decreasing amplitude. Subjects were asked to indicate the direction of motion in three conditions: vestibular only, subjects roll tilted in the dark; visual only, a visual scene was tilted in front of the subjects; and combined visual + vestibular, subjects rotated while watching a stationary visual scene. For each subject, we calculated the percentage difference between the threshold for combined visual/vestibular stimuli and the best of either the vestibular or visual threshold. Results: Visual and vestibular thresholds significantly differed in function of frequency. Conclusion: Vestibular and visual thresholds at different frequencies are significantly different, which support the fact that they use different perception pathways. The brain may determine the body motion in space during roll tilt motion by integration of vestibular and visual inputs: the combined estimate of motion is better than the vestibular input and is not significantly better than the visual cues alone. This research may be useful in the workup of vertiginous disorders with impaired integration of vestibular and visual cues (motion sickness and migraine dizziness).