Development of a novel 6-DOF parallel mechanism moving platform for investigating the effects of multimodal sensory feedback information regarding postural stability in humans

The purpose of this study was to develop a six-degree-of-freedom parallel mechanism moving platform to investigate the effects of multimodal sensory feedback information while standing upright. We constructed a custom-designed disturbance-applying instrument (DAI) consisting of a support surface suspended from eight pneumatic artificial muscles. The posture of the support surface was controlled with a proportional–integral–derivative (PID) feedback system using an infra-red camera-based real-time 3D motion capture system, and was estimated by step and frequency responses. Head trajectories of two healthy subjects were recorded to evaluate the effect of the differences in the impedance of the support surface during upright standing with their eyes opened/closed. The results demonstrated that the step and frequency responses of the DAI were good enough to enhance the bodily oscillation and head motion relative to the support surface. Indeed, the head-swaying space, using the DAI in a 0.2-Hz air-supplying condition during upright standing with their eyes closed, was larger than in the other standing condition. These results suggest that the specific medio-lateral head swaying was caused by the effects of the multimodal sensory feedback information using the DAI. In conclusion, we developed a novel moving platform to investigate the effects of multimodal sensory feedback information upon upright postural control. The DAI would be particularly valuable to enhance the head-swaying space during upright standing by changing the impedance of the support surface or stimulating the translational and/or rotational sensory feedback integration.