The human sound-evoked vestibulo-ocular reflex and its electromyographic correlate

Sound-evoked responses from a normal control (left panels) and from a subject with right-sided superior canal dehiscence (right panels). Note that the scales differ to account for the 5–10× greater magnitude of responses in SCDS compared with controls. The interrupted line marks stimulus onset. Ipsilateral and contralateral traces are colored gray and black, respectively. The OVEMP in both subjects is a contralaterally predominant, negative–positive potential. Eye velocity and position traces for the normal subject show a brief upward followed by a downward vertical movement. In SCDS, an upward vertical and contraversive torsional eye movement is seen. Eye movement onset coincides with the OVEMP peak. Although stimulus artifacts are present in the eye movement traces, they end before the physiologic eye movement begins.

Left right and binaural stimulation of a subject with bilateral SCDS. On monaural stimulation, both eyes move in plane with the superior canal on the stimulated side. On binaural stimulation, each eye maps to the dehiscent canal on the contralateral side. Torsional eye movement is depicted from the viewer’s perspective.

The bargraphs represent OVEMP peak-to-peak amplitudes for three gaze conditions (up/straight ahead/down), for the ipsilateral (white) and contralateral (black) eyes, for air- and bone-conducted sound. As subjects look down OVEMP amplitude falls and symmetry increases.

The traces show eye-in-head displacement, velocity, VOR magnitude and OVEMPs for upgaze, straight ahead and downgaze in a single R sided SCDS subject, upon R ear stimulation. The magnitude of the OVEMP is profoundly influenced by gaze and the VOR magnitude is unaffected. As the subjects look down, the torsional eye velocity component decreases, the vertical component increases.

Comparison of sound and vibration-evoked OVEMP and VOR in a normal control. The eye displacement, eye velocity change and the OVEMP are twice as large in response to vibration.

A single subject with R SCDS is stimulated by tones ranging from 250 to 2000Hz. OVEMP and VOR show concordant modulation, with maximal magnitudes at 500Hz for both responses. Only traces for the contralateral eye are depicted.