the axes of the involved canals. Using this premise, one can stimulate the vestibular system in numerous ways (lowand high-velocity head movements in 3-D, 3-D calorics, and diverse methods of inducing positional nystagmus) and relate the resulting eye movements to the function or dysfunction of single SCCs [44–46].

Obviously, in humans one cannot stimulate with electrodes the vestibular nerve and record the resulting eye movements. We therefore tested patients in whom nature produced a situation where just one SCC is stimulated. These patients suffered from benign paroxysmal positioning nystagmus. When the nystagmus induced by positioning the subject in the offending position is measured in 3-D and the average axis of eye rotation is reconstructed and plotted into a head-fixed reference system together with the anatomical on-directions of the SCCs it can be shown that the elicited eye movements are closely aligned with the direction of the offending canal. With this proof that also in humans eye movements are produced in the plane of the stimulated SCC, it is possible to deduct which canals are responsible for the direction of eye movements found during vestibular stimulation when parts of the vestibular sensors are defective [44, 47, 48].

Otolith Function

Subjective Visual Vertical

The subjective visual vertical (SVV) is a sensitive measure of otolith and especially utricular function. The bilateral graviceptive input from the otoliths dominates our perception of verticality. To test for SVV, the subjects sit with their heads fixed in the upright position and look at an illuminated line (on computer display or projected with a laser galvanometer system) in complete darkness. They then have to adjust 10 times separately for each eye the line from different starting positions to their SVV. In acute peripheral vestibular lesions, including the utricles, there is an ipsiversive deviation of the SVV of about 10–15 . Likewise, most patients with acute unilateral brainstem infarctions exhibit pathological tilts of static SVV from the true vertical [49].

Click-Evoked Myogenic Potentials

Electromyograms can be recorded from surface electrodes over the sternomastoid muscles and averaged in response to brief (0.1-ms) clicks played through headphones. In normal subjects, clicks 85–100 dB above 45 dB SPL (perceptual threshold for normal subjects) evoke reproducible changes in the