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. (C) 1997 Elsevier Science Ireland Ltd.