Noise-induced transitions in human postural sway

Abstract

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.

Human Balance Control: Dead Zones, Intermittency, and Micro-chaos

“…These differences become most apparent when the structures shown, respectively, in Figures 5b and d are hung at their stable (downward) positions [90]. Whereas (18) predicts that the oscillations occur about the pivot point, (28) predicts that they occur near the mid-point of the pendulum as observed experimentally [48]. Moreover, the period of the oscillations predicted by (18) …”

“…The first modeling attempt to consider the effects of a dead zone on postural sway was developed in 1996 by Eurich and Milton [28]. They made four assumptions: 1) the postural sway control mechanisms are over damped; 2) the proprioceptive system involved in balance control is activated only when the angle exceeds a threshold; 3) the corrective feedback acts maximally within a very small ranges of angle; and 4) the angular displacements are very small and hence ℓ sin θ ≈ x, where x is the displacement in the x-direction.…”

“…Moreover, experimental paradigms using piecewise constant types of feedback can be developed and used to directly compare prediction with observation [51,52,58,72,64]. (20) observed as a function of C and τ (see [28] for details).…”

“…In general there can be a different threshold associated with each of θ(t),θ(t) andθ(t); however, here we have shown only a threshold for θ(t). In the mathematical literature, the study of the effects of a threshold on feedback control falls under the heading of switching [31,45,28], or hybrid [35] control. The threshold is a strong small-scale nonlinearity since it destroys the fixed-point.…”

Modelling human balance using switched systems with linear feedback control

“…Further research is needed to design experimental tests that can help to discriminate between different control models. An alternative model for human postural sway was considered in Eurich & Milton [20]. In this work, the authors use a reduced first-order model with a timedelayed feedback.…”