Direct current galvanic vestibular stimulation modulates sound localization abilities

The vestibular system has been shown to play a role in the integration of spatial sensory information. For instance, vestibular perturbations induce significant shifts in spatial tactile tasks, but results have been contradictory regarding auditory modality. This observation may be because some of the previous vestibular stimulation methods (i.e., stochastic GVS) did not reliably induce a self-motion effect. This study aims to evaluate the importance of directional illusory motion on auditory localization mechanism, using direct current GVS. Twenty young healthy participants performed a sound localization task under earphones with 9 positions in the azimuth plane divided into three quadrants 7Left (45°;- 30°;- 20°), Center (- 10°;0°;10°), and Right (20°;30°;45)]. Participants were asked to verbally identify the exact position of the sound source under 3 conditions: (1) Without GVS (2) GVS with anode on the right mastoid (3) GVS with anode on the left mastoid. Results were analyzed using the non-parametric Friedman test and Wilcoxon rank-sum post-hoc test with a Bonferroni correction applied to account for multiple comparisons. Compared to baseline, left anodal stimulation caused a greater error ratio for sounds in all quadrants. Moreover, for sounds in the right quadrant, a significantly greater error ratio was observed for anode left compared to the anode right condition. Right anodal condition caused a greater error ratio for sounds in the left and the center quadrants compared to the baseline condition. This study demonstrates for the first time, that sound source localization can be influenced by direct current GVS and is modulated according to the anode position.