Supplementary material from "Angular distribution of fractal temporal correlations supports adaptive responses to wobble board instability"

Contemporary models of human postural control propose an intermittent controller regulating the postural center of pressure (CoP) about a stable saddle-shaped manifold along anatomical anteroposterior (AP) and mediolateral (ML) axes, releasing CoP in an outwards spiral when inactive. Experimental manipulations can evoke this saddle-type topology in fractal temporal correlations along the AP axis and reducing correlations along the ML axis. We tested how instability and attentional load influence postural control across the full angular range of fractal variability along the 2D support surface. Stable, quiet standing exhibited classic saddle-like topology, with stronger fractal temporal correlations in CoP fluctuations along AP axes. The attentional demand of TMT did not affect angular variation or strength of fractal temporal correlations across the 2D support surface. However, maintaining an upright balance on a wobble board reshaped and reoriented the angular distribution of fractal temporal correlations, accentuating saddle-like angular variation and rotating the strongest fractal temporal correlations predominantly along the ML axis. Stabilizing posture in the face of wobble board instability prompted the saddle-type angular distribution of fractal temporal correlations. These findings underscore the significance of multifractality in defining control parameters that govern postural stability across the full angular range of the 2D support surface.