Can explicit visual feedback of postural sway efface the effects of sensory manipulations on mediolateral balance performance?

Explicit visual feedback on postural sway is often used in balance assessment and training. However, up-weighting of visual information may mask impairments of other sensory systems. We therefore aimed to determine whether the effects of somatosensory, vestibular, and proprioceptive manipulations on mediolateral balance are reduced by explicit visual feedback on mediolateral sway of the body center of mass and by the presence of visual information. We manipulated sensory inputs of the somatosensory system by transcutaneous electric nerve stimulation on the feet soles (TENS) of the vestibular system by galvanic vestibular stimulation (GVS) and of the proprioceptive system by muscle-tendon vibration (VMS) of hip abductors. The effects of these manipulations on mediolateral sway were compared with a control condition without manipulation under three visual conditions: explicit feedback of sway of the body center of mass (FB), eyes open (EO), and eyes closed (EC). Mediolateral sway was quantified as the sum of energies in the power spectrum and as the energy at the dominant frequencies in each of the manipulation signals. Repeated-measures ANOVAs were used to test effects of each of the sensory manipulations, of visual conditions and their interaction. Overall, sensory manipulations increased body sway compared with the control conditions. Absence of normal visual information had no effect on sway, while explicit feedback reduced sway. Furthermore, interactions of visual information and sensory manipulation were found at specific dominant frequencies for GVS and VMS, with explicit feedback reducing the effects of the manipulations but not effacing these.