Otolith-ocular response during low-frequency linear acceleration

Background. During constant velocity rotation about the earth's vertical ax is, eccentric displacement of the head can be used to generate adequate sti mulation of the otolith organs. More recently, studies have been performed with a variable radius rotatory chair, which permits a controlled modulatio n of the centripetal or radial acceleration,to achieve linear acceleration frequencies much lower than with a conventional linear sled. Methods. In the present study, frequency response and threshold testing was performed using sinusoidal modulation of the chair radius. Three-dimension al eye movements were recorded with binocular video-oculography. Results. The gain (0.09 degrees/degrees at 0.03 Hz, 0.009 degrees/degrees a t 1 Hz) and phase relationships of the otolith-ocular response (OOR) show a low-pass characteristic over the measured range of 0.03-1.0 Hz. In compari son to the flat response of neurophysiological recordings from the otolith afferent,our findings support the idea that any low-pass filtering of otoli th afferents occurs at the level of the vestibular nuclei. Conclusion. The OOR could be detected at acceleration levels of 0.03 m/s(2) , much lower than the subjective threshold for the perception of 0.08 m/s(2 ).