The effect of additional hand contact on postural stability perturbed by a moving environment

Additional hand contact of external objects has been shown to reduce postural instability caused by a deficiency of one or more senses. Little is known, however, if additional contact can help in an environment where the senses are available but conflicting. This question was investigated by analyzing the effect of different types of hand contact on postural stability perturbed by the moving visual scene. While standing for 1 min on a rocker board in front of a screen, eight healthy young subjects observed a projection of a virtual ship rocking on water to simulate standing on the ship's deck. In randomly assigned trials subjects were asked (a) to stand with arms at sides (with no contact); (b) to hold a standard cane parallel to the ground; (c) to lightly touch a rocker cane handle with their index finger; or (d) touch a standard quad cane handle with their index finger. Based on the kinematic data collected, the displacement of the center of mass (COM) and angular displacements in the hip and ankle joints were computed. Results showed that the moving visual scene perturbed body stability. However, additional contact with support of varying stability reduced the destabilizing effect. The results can be potentially used for practical purposes; when in an environment with visual perturbations simply holding an object in hand may help stabilize the body when at risk for a fall.