Stabilometric signal analysis in tests with sound stimuli.

Posture control is mediated by the integration between the environment information (coming from the visual, somatosensory and vestibular systems) and the efferent organs (motoneurons and muscles). The influence of the first systems on body sway signals is already documented in the literature. Few studies are focused in the relationship between stabilometric signals (objective measure of stability) and vestibular stimulation, due to the difficulty in achieving a specific and independent stimulation of this system. The present study sought to examine this aspect, proposing high intensity sounds as a way to perturb the vestibular system, based on vestibular evoked myogenic potentials theory. Sixty-six volunteers were submitted to a variety of sound stimulation conditions (pure tones, clicks and bursts) while they stayed in upright position on a force platform. The variables recorded were mean position, mean standard deviation, mean velocity, mean displacement, mean frequency (all of them in lateral and anterior-posterior directions) and sway area. Values obtained in each variable were treated by an analysis of variance (ANOVA). Results confirmed the influence of visual system in the mean velocity of center of pressure. No statistic difference was found when conditions with and without sound stimulation were compared by ANOVA at the same visual condition with any type of sound. However, visual analysis of the plot of mean lateral displacement and anterior-posterior standard deviation shows some consistent patterns of change during the recovery phase after stimulation, confirmed, sometimes, by Wilcoxon test. This result shows that balance is not always influenced by the types of sound stimulation used in this work. It encourages future experiments setting louder intensities, as well as other sources of stimulus that could affect vestibular receptors (direct or indirectly), to search for specific modifications in the stabilometric signal.