The role and interaction of visual and auditory afferents in postural stability

Background: Maintaining balance requires the integration of vestibular, proprioceptive and visual information and the translation of this input into appropriate motor responses. Although the role of the visual system has been widely investigated, there are no studies addressing the influence of non-specific distracting auditory inputs on postural stability. Objective: To analyze the role of the visual and auditory systems in the maintenance of postural stability and to assess potential interaction between the two sensory systems. Methods: Twenty-three healthy subjects were examined by computerized dynamic posturography. Stability index scores were calculated under each of six conditions: three visual conditions (sway feedback, eyes open without feedback, eyes closed) were combined with two auditory conditions (exposure or no exposure to non-specific auditory input). Analysis of variance (ANOVA) was used to test for differences among groups in the six test conditions. Results: Postural stability was much poorer in the eyes-closed (overall stability index (OSI): 6.8 +/- 2.1 degrees) than in the eyes-open condition (OSI: 2.2 +/- 1.2 degrees). Balance control significantly improved with visual feedback (OSI: 1.2 +/- 0.5 degrees). Exposure to non-specific auditory input (music through headphones) did not have a significant influence (OSI: 6.4 +/- 2.3 degrees/2.0 +/- 0.9 degrees/1.1 +/- 0.5 degrees). Conclusions: Postural stability depended not only on whether the subjects were tested with their eyes open or closed but also on the presence or absence of visual feedback. Non-specific auditory information did not influence postural control. Since postural stability is regulated by multiple senses such as the vestibular system and proprioception, auditory stimuli may play an increasing role if one of the systems involved is impaired. (C) 2009 Elsevier B.V. All rights reserved.