Effect of galvanic vestibular stimulation on perception of subjective vertical in standing humans

The present work reinvestigated the influence of bimastoidal galvanic vestibular stimulation (0.4 mA during 10 sec.) on subjective vertical. We tested the hypothesis that deviations are directed towards the anode side, like postural tilt evoked by galvanic vestibular stimulation. 15 subjects were instructed to orient vertically in darkness a light-rod during 3 experimental conditions of control, anode right, and anode left. The statistical analysis showed that the perception of the vertical was modified according to the experimental conditions and the subjects. Angular deviations occurred toward the anode side. The results are interpreted as a consequence of a modification of the central representation of the vertical or of ocular torsion directed towards the anode side and likely to induce an apparent displacement of the rod towards the cathode side.