Correlation dimension estimates of human postural sway

Date

2013-02-01

Author

Gürses, Senih

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

96
views

0
downloads

Human postural sway during quiet standing demonstrates a complex structured dynamics, which has been studied by applying numerous methods, such as linear system identification methods, stochastic analysis, and nonlinear system dynamics tools. Although each of the methods applied revealed some particular features of the sway data none of them have succeeded to present a global picture of the quiet stance dynamics, which probably has both stochastic and deterministic properties. In this study we have started applying ergodic theory of dynamical systems to explore statistical characteristic of the sway dynamics observed in successive trials of a subject, different subjects in an age group, and finally different age groups constituted by children, adults, and elderly subjects. Five successive 180-s long trials were performed by each of 28 subjects in four age groups at quiet stance with eyes open. Stationary and ergodic signal characteristics of five successive center of pressure time series collected from a subject in antero-posterior direction (CoPx) were examined. 97% of the trials were found to be stationary by applying Run Test while children and elderly groups demonstrated significant nonstationary behavior. On the other hand 13 out of 24 subjects were found to be nonergodic. We expected to observe differences in complexity of CoPx dynamics due to aging (Farmer, Ott, & Yorke, 1983). However linear metrics such as standard deviation and Fourier spectra of CoPx signals did not show differences due to the age groups. Correlation dimension (D-k) estimates of stationary CoPx signals being an invariant measure of nonlinear system dynamics were computed by using the average displacement method (Eckmann & Ruelle, 1985). Postural dynamics was expanded in m-dimensional space through CoPx signal by introducing optimum time delays, tau(critical). 112 out of 136 stationary CoPx signals for 24 stationary subjects converged to D-k estimates. Average of D-k estimates for children and adult groups was 3.67 +/- 0.28, whereas mean of D-k estimates for elderly subjects was 4.12 +/- 0.59. Nonlinear metrics of postural sway (tau(critical), m(saturated). and D-k estimates) showed significant differences with respect to the age groups. D-k estimates computed from ergodic subjects' CoPx sway trajectories revealed that human quiet standing demonstrates multiple degree of freedom dynamics having a fractal structure with a considerable level of noise embedded in the signal whose characteristics is determined individually for each subject. Furthermore by using ergodic theory of complex systems, we have been able to show that the ability to independently control multiple degrees of freedom has been affected by aging.

Subject Keywords

Postural sway, Center-of-pressure, Ergodicity, Correlation dimension, Optimum time delay, Aging

URI

https://hdl.handle.net/11511/37946

Journal

HUMAN MOVEMENT SCIENCE

DOI

https://doi.org/10.1016/j.humov.2012.07.007

Collections

Department of Engineering Sciences, Article

Suggestions

OpenMETU
Core

Dynamic performances of kinematically and dynamically adjustable planar mechanisms İyiay, Erdinç; Soylu, Reşit; Department of Mechanical Engineering (2003) In this thesis, the dynamic performances of kinematically and dynamically adjustable planar mechanisms have been investigated. An adjustable mechanism is here defined to be a mechanism where some of the kinematic and/or dynamic parameters are changed in a controlled manner in order to optimize the dynamic behaviour of the mechanism in spite of variable operating conditions. Here, variable operating conditions refer to variable load(s) on the mechanism and/or variable desired input motion. The dynamic behavi...
Performance Evaluation of the Numerical Flux Jacobians in Flow Solution and Aerodynamic Design Optimization Ezertas, Alper; Eyi, Sinan (2010-07-16) A direct sparse matrix solver is utilized for the flow solution and the analytical sensitivity analysis. The effects of the accuracy of the numerical Jacobians on the accuracy of sensitivity analysis and on the performance of the Newton's method flow solver are analyzed in detail. The gradient based aerodynamic design optimization is employed to demonstrate those effects.
Diffusion Tensor Imaging Group Analysis Using Tract Profiling and Directional Statistics Metin, Mehmet Ozer; Gökçay, Didem (2021-03-01) Group analysis in diffusion tensor imaging is challenging. Comparisons of tensor morphology across groups have typically been performed on scalar measures of diffusivity, such as fractional anisotropy (FA), disregarding the complex three-dimensional morphologies of diffusion tensors. Scalar measures consider only the magnitude of the diffusion but not directions. In the present study, we have introduced a new approach based on directional statistics to use directional information of diffusion tensors in sta...
Assessment of dynamic response FD algorithms by beam and plate FE computations Alaylioglu, H.; Oral, Süha; Alaylıoğlu, Ayşe (Elsevier BV, 1988-10) Improvement in understanding of the process of direct integration of the equations of motion through numerical dissipation parameter interaction is being regarded as one of the significant achievements of structural dynamics research over the past quarter century. The numerical software fraternity has extended one-step integration algorithms, emphasizing controllable approximation characteristics with respect to such factors as period elongation and amplitude decay. These studies have resulted in setting up...
Interaction network effects on position- and velocity-based models of collective motion Turgut, Ali Emre; Okay, Ilkin Ege; Ferrante, Eliseo; Huepe, Cristian (The Royal Society, 2020-08-01) We study how the structure of the interaction network affects self-organized collective motion in two minimal models of self-propelled agents: the Vicsek model and the Active-Elastic (AE) model. We perform simulations with topologies that interpolate between a nearest-neighbour network and random networks with different degree distributions to analyse the relationship between the interaction topology and the resilience to noise of the ordered state. For the Vicsek case, we find that a higher fraction of ran...

Citation Formats

S. Gürses, “Correlation dimension estimates of human postural sway,” HUMAN MOVEMENT SCIENCE, pp. 48–64, 2013, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/37946.