Perception of threshold-level whole-body motion during mechanical mastoid vibration.

BACKGROUND: Vibration applied on the mastoid has been shown to be an excitatory stimulus to the vestibular receptors, but its effect on vestibular perception is unknown. OBJECTIVE: Determine whether mastoid vibration affects yaw rotation perception using a self-motion perceptual direction-recognition task. METHODS: We used continuous, bilateral, mechanical mastoid vibration using a stimulus with frequency content between 1 and 500 Hz. Vestibular perception of 10 healthy adults (M +/- S.D. = 34.3 +/- 12 years old) was tested with and without vibration. Subjects repeatedly reported the perceived direction of threshold-level yaw rotations administered at 1 Hz by a motorized platform. A cumulative Gaussian distribution function was fit to subjects' responses, which was described by two parameters: bias and threshold. Bias was defined as the mean of the Gaussian distribution, and equal to the motion perceived on average when exposed to null stimuli. Threshold was defined as the standard deviation of the distribution and corresponded to the stimulus the subject could reliably perceive. RESULTS: The results show that mastoid vibration may reduce bias, although two statistical tests yield different conclusions. There was no evidence that yaw rotation thresholds were affected. CONCLUSIONS: Bilateral mastoid vibration may reduce left-right asymmetry in motion perception.