[External Intervention for Visually Induced Postural Change during Video Viewing].

Objectives: Virtual reality (VR) and three-dimensional (3D) images have become increasingly popular. It has been reported that visually induced motion sickness (VIMS) is more frequently caused by viewing these images. We propose a method to control VIMS by controlling visually evoked postural responses (VEPRs) using galvanic vestibular stimulation (GVS). In this study, we focused on the effect of VEPRs on body sway and conducted a transfer function analysis between the GVS and body sway. On the basis of the results of this investigation of the causes of VIMS, countermeasures must be considered.

Methods: The experiment involved 15 healthy young adults, comprising six males and nine females, all aged 21 years. The subjects were asked to maintain a Romberg posture while viewing an image that included a large number of randomly positioned moving spheres with their peripheral vision. In addition, body sway during GVS as an external stimulus was measured for 120s for each task.

Results: The transfer function analysis of the body sway showed that the influence on the equilibrium function was significantly enhanced not only by the GVS but even more so by viewing the video clips synchronized to the GVS.

Conclusions: GVS current signals induced body sway and increased the width of body sway synergistically. It was also suggested that a time delay structure occurred between the GVS current signal and body sway.