Velocity dependence of sensory reweighting in human balance control.

The relative contributions of proprioceptive, vestibular, and visual sensory cues to balance control change depending on their availability and reliability. This sensory reweighting is classically supported by nonlinear sway responses to increasing visual surround and/or surface tilt amplitudes. However, recent evidence indicates that visual cues are reweighted based on visual tilt velocity rather than tilt amplitude. Therefore, we designed a study to specifically test the hypothesized velocity dependence of reweighting while expanding on earlier findings for visual reweighting by testing proprioceptive reweighting for standing balance on a tilting surface. Twenty healthy young adults stood with their eyes closed on a toes-up/-down tilting platform. We designed four pseudorandom tilt sequences with either a slow (S) or a fast (F) tilt velocity and different peak-to-peak amplitudes. We used model-based interpretations of measured sway characteristics to estimate the proprioceptive sensory weight ( W prop ) within each trial. In addition, root-mean-square values of measured body center of mass sway amplitude (RMS) and velocity (RMSv) were calculated for each tilt sequence. W prop , RMS, and RMSv values varied depending on the stimulus velocity, exhibiting large effects (all Cohen's d >1.10). In contrast, we observed no significant differences across stimulus amplitudes for W prop (Cohen's d : 0.02-0.16) and, compared with the differences in velocity, there were much smaller changes in RMS and RMSv values (Cohen's d : 0.05-0.91). These results confirmed the hypothesized velocity, rather than amplitude, dependence of sensory reweighting. NEW & NOTEWORTHY This novel study examined the velocity dependence of sensory reweighting for human balance control using support surface tilt stimuli with independently varied amplitude and velocity. Estimates of the proprioceptive contribution to standing balance, derived from model-based interpretations of sway characteristics, showed greater sensitivity to changes in surface tilt velocity than surface tilt amplitude. These results support a velocity-based mechanism underlying sensory reweighting for human balance control.