Galvanic vestibular stimulation in humans: effects on otolith function in roll

The effects of unilateral galvanic vestibular stimulation on (1) ocular torsion, (2) subjective tilt of the peripheral visual field, and (3) subjective tilt of a foveal vertical line were measured in 12 healthy subjects. A rectangular, unipolar binaural electric current was applied to the subject' s mastoid. Anodal stimulation of the right mastoid led to an ipsiversive tonic ocular torsion (0.5-3.7 degrees) and to a contralateral tilt of both the peripheral visual field (1-9 degrees), and a foveal vertical line (0.5-6.2 degrees). There was a correlation between the amount of the three measured parameters and the strength of the applied current. Static ocular torsion, central and peripheral visual tilts represent stimulus-induced tonic otolith imbalance between the two labyrinths. Thus, galvanic vestibular stimulation not only affects dynamic semicircular canal input but also static otolith input in the roll plane.