Attenuation of the visual control of balance under virtual postural threat


Background: Virtual reality (VR) can be used to induce the sensation of self-motion. In presenting a visual stimulus to elicit balance correcting responses, the visual control of balance may be evaluated. It is unclear what type of visual stimulus should be presented to optimally perturb balance and whether subsequent responses are influenced by a threat to posture. Objectives: 1. Explore stimuli relevant for the visual control of balance in VR. 2. Determine whether the use of vision for balance control is influenced by postural threat. Methods: 32 healthy, young adults (18 males) completed 5-minute, standing trials in VR with LOW (0m) and HIGH (7m) height conditions. A continuous, stochastic visual stimulus (frequencies: 0-1Hz, amplitude: +/-5cm) was presented as an anteroposterior translation. Outcome measures included center of pressure (COP), kinematic displacements, electromyography, psychological states, and electrodermal activity (EDA). Results: Significant coherence (between stimulus and COP) was observed across frequencies (~0.2-1Hz) at both LOW and HIGH. There was no difference of coherence between conditions, however, the gain was significantly larger at ~0.4Hz for LOW. Two cumulant density peaks were identified (~0.5s and ~1.9s) with significantly larger amplitudes observed in the LOW condition. At HIGH, there were significant increases in reported anxiety, fear, and EDA, and significant decreases in perceived stability and confidence, when compared to LOW. Conclusions: A wide range of frequencies relevant for the visual control of balance were identified with the stochastic visual stimulus. Results suggest a decrease in the sensory gain of the visual system under postural threat.

Acknowledgments: The authors acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).