Human Postural Control : Force Plate Experiments

We report the results of time series analysis of human body sway while quiet upright stance. The bivariate records (stabilograms) are measured by means of a force plate. To investigate interrelations between oscillations in anterior{posterior and lateral directions we use several techniques: cross-spectrum analysis, generalized mutual information, and calculation of instantaneous relative phase. We nd that the stabilograms can be qualitatively rated into two groups: noisy and oscilla-tory patterns. Further, we show that oscillatory patterns may demonstrate phase locking. We argue that these patterns are due to stochastic and chaotic dynamics, respectively. We discuss the plausible strategy of postural control and present the model that qualitatively describes transitions from noisy to oscillatory patterns and phase synchronization. The relevance of the results of the time series analysis for the diagnostics of neurological pathologies is discussed.