Noise-induced transitions in human postural sway

Correlation functions with multiple scaling regions occur in the description of the fluctuations in the center of pressure during quiet standing. Postural sway is modeled as an inverted pendulum with a delayed feedback constructed such that for deviations beyond a spatial threshold a constant restoring force is engaged. In the absence of noise, two stable limit cycles coexist. The correlation function depends on the added noise intensity: at intermediate noise levels three scaling regions appear whereas only two occur for high noise levels. Our observations suggest that correlation functions with multiple scaling regions reflect noise-induced transitions in bistable dynamical systems.