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Transition from persistent to anti-persistent correlations in postural sway indicates velocity-based control.

Delignières D, Torre K, Bernard PL - PLoS Comput. Biol. (2011)

Bottom Line: In this paper, we discuss the conclusions drawn from previous analyses of COP dynamics using fractal-related methods.A simple model for COP velocity dynamics, based on a bounded correlated random walk, reproduces the main statistical signatures evidenced in the experimental series.The implications of these results are discussed.

View Article: PubMed Central - PubMed

Affiliation: EA 2991 Movement To Health, Montpellier-1 University, Euromov, Montpellier, France. didier.delignieres@univ-montp1.fr

ABSTRACT
The displacement of the center-of-pressure (COP) during quiet stance has often been accounted for by the control of COP position dynamics. In this paper, we discuss the conclusions drawn from previous analyses of COP dynamics using fractal-related methods. On the basis of some methodological clarification and the analysis of experimental data using stabilogram diffusion analysis, detrended fluctuation analysis, and an improved version of spectral analysis, we show that COP velocity is typically bounded between upper and lower limits. We argue that the hypothesis of an intermittent velocity-based control of posture is more relevant than position-based control. A simple model for COP velocity dynamics, based on a bounded correlated random walk, reproduces the main statistical signatures evidenced in the experimental series. The implications of these results are discussed.

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Graphical signatures of cross-over.Schematic representation of the typical log-log diffusion plots resulting from SDA and DFA. This figure illustrates how the cross-over phenomenon can be detected using diffusion analysis.
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pcbi-1001089-g002: Graphical signatures of cross-over.Schematic representation of the typical log-log diffusion plots resulting from SDA and DFA. This figure illustrates how the cross-over phenomenon can be detected using diffusion analysis.

Mentions: Figure 2 shows a schematic representation of typical diffusion plots obtained with SDA and DFA. Obtaining an inflection point in the diffusion plot (Figure 2, right graph), with slope values changing from greater than to less than the above-cited boundary values, indicates the so-called cross-over phenomenon. It shows a transition from persistent correlations on short observation scales to anti-persistent correlations on longer observation scales in the corresponding differenced series, thereby indicating that the latter is bounded within given limits [20]: the bounded variable derives (i.e., is positively correlated) until reaching a given limit value. At this point, the fluctuations reverse in direction (i.e., the series becomes negatively correlated). Such bounding suggests that the variable concerned is (in)directly controlled. Note that bounded series are obviously stationary (at least in the long term), but cannot be considered as genuine fGn.


Transition from persistent to anti-persistent correlations in postural sway indicates velocity-based control.

Delignières D, Torre K, Bernard PL - PLoS Comput. Biol. (2011)

Graphical signatures of cross-over.Schematic representation of the typical log-log diffusion plots resulting from SDA and DFA. This figure illustrates how the cross-over phenomenon can be detected using diffusion analysis.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3044760&req=5

pcbi-1001089-g002: Graphical signatures of cross-over.Schematic representation of the typical log-log diffusion plots resulting from SDA and DFA. This figure illustrates how the cross-over phenomenon can be detected using diffusion analysis.
Mentions: Figure 2 shows a schematic representation of typical diffusion plots obtained with SDA and DFA. Obtaining an inflection point in the diffusion plot (Figure 2, right graph), with slope values changing from greater than to less than the above-cited boundary values, indicates the so-called cross-over phenomenon. It shows a transition from persistent correlations on short observation scales to anti-persistent correlations on longer observation scales in the corresponding differenced series, thereby indicating that the latter is bounded within given limits [20]: the bounded variable derives (i.e., is positively correlated) until reaching a given limit value. At this point, the fluctuations reverse in direction (i.e., the series becomes negatively correlated). Such bounding suggests that the variable concerned is (in)directly controlled. Note that bounded series are obviously stationary (at least in the long term), but cannot be considered as genuine fGn.

Bottom Line: In this paper, we discuss the conclusions drawn from previous analyses of COP dynamics using fractal-related methods.A simple model for COP velocity dynamics, based on a bounded correlated random walk, reproduces the main statistical signatures evidenced in the experimental series.The implications of these results are discussed.

View Article: PubMed Central - PubMed

Affiliation: EA 2991 Movement To Health, Montpellier-1 University, Euromov, Montpellier, France. didier.delignieres@univ-montp1.fr

ABSTRACT
The displacement of the center-of-pressure (COP) during quiet stance has often been accounted for by the control of COP position dynamics. In this paper, we discuss the conclusions drawn from previous analyses of COP dynamics using fractal-related methods. On the basis of some methodological clarification and the analysis of experimental data using stabilogram diffusion analysis, detrended fluctuation analysis, and an improved version of spectral analysis, we show that COP velocity is typically bounded between upper and lower limits. We argue that the hypothesis of an intermittent velocity-based control of posture is more relevant than position-based control. A simple model for COP velocity dynamics, based on a bounded correlated random walk, reproduces the main statistical signatures evidenced in the experimental series. The implications of these results are discussed.

Show MeSH
Related in: MedlinePlus