The effect of two types of virtual reality on voluntary center of pressure displacement.

Voluntary movements result in internal perturbations of balance and equilibrium. One variable regulated during movement is the position of the center of pressure (COP). Sensory information from the visual, vestibular and somatosensory systems is used in establishing relevant frames of reference for postural control. In this study, we were interested in determining whether different limitations of COP movement occur when different approaches to delivering virtual environments are used and when visual information incoherent with vestibular and somatosensory information is provided. Eighteen healthy adults completed voluntary lateral reaches under three conditions: continuous lateral reach (CLR), flatscreen virtual reality (FS), and head-mounted display virtual reality (HMD). Reaching behavior was indexed by force plate measures of maximum anterior-posterior and lateral displacement of the COP. The COP movement decreased in the lateral direction in the HMD condition relative to the FS. The maximum range of COP movement in the anterior-posterior direction increased as a function of reaching task with HMD realizing the greatest amount of movement. The lack of an exocentric frame of reference in HMD coherent with information from other sensory systems results in limiting COP movement within the base of support (BOS) in order to decrease the challenge to the postural control system.