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J. G. Milton, T. Insperger, W. Cook, D. M. Harris and G. Stepan . 2018. Microchaos in human postural balance: Sensory deadzones and sampled time-delayed feedback. Physical Review E 98: 022223. Full Article

Models for the stabilization of an inverted pendulum figure prominently in studies of human balance control. Surprisingly, fluctuations in measures related to the vertical displacement angle for quietly standing adults with eye closed exhibit chaos. Here we show that small amplitude chaotic fluctuations (``microchaos'') can be generated by the interplay between three essential components of human neural balance control, namely, time-delayed feedback, a sensory dead zone and frequency-dependent encoding of force. When the sampling frequency of the force encoding is decreased, the sensitivity of the balance control to changes in the initial conditions increases. The sampled, time-delayed nature of the balance control may provide insights into why falls are more common in the very young and the elderly.

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