Multisensory interactions in the automatic control of postural sway

Visual motion signals are an important source of self-motion information that are used in postural control. Bronstein and Buckwell (Exp. Brain Res. 113, 243–248, 1997) showed that postural reactions to visual motion are not rigid responses to optokinetic stimulation but specific responses appropriate for stabilising posture in natural circumstances: body sway, for instance, was abolished when participants fixated a static object in front of a laterally moving background, which in itself induced sway. We test whether haptic and auditory as well as visual fixation points reduce body sway induced by a background that either moved left/right or forward/back on a large (3 × 7 m) 3D visual display. 10 participants were asked to respond when a fixation target, whichs was presented either on a background or foreground, changed colour. Body sway was measured using a VICON motion tracking system. We tested three conditions that replicated Bronstein and Buckwell’s original study and show that body sway, induced by lateral motion of the background is abolished when participant fixate on a (virtual) foreground object. We extended their study by showing that 3D motion (looming/receding background) has a similar effect to lateral motion and to show that body sway can be effectively reduced by providing either auditory (a loudspeaker emitting a white noise) and haptic (participants lightly touch a tripod with their index finger) cues. Our findings show that postural control draws auditory and haptic as well as visual cues. The findings are relevant to the design of virtual reality systems and provide a method for objective measures of presence in virtual environments.