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Figure 2

From: Advantages and problems of nonlinear methods applied to analyze physiological time signals: human balance control as an example

Figure 2

Time signals and Higuchi dimensions. (a) Typical COP sway during two-footed stand with open eyes (TFOE) in y-direction (S y ). 30,000 data points were sampled with a frequency of 500 Hz in 60 s. The insert in the figure shows an enlargement of the signal. This easy task is associated with small elongations. Standard deviation (SD) was 0.74 mm (SD of noise was 0.05 mm) resulting in a signal-to-noise ratio (SNR) of 14.8. (b) Higuchi dimension D H as a function of time (black graph; gliding box length l = 3000 data points; D H ranged from 1.30 to 1.62), and for the entire time signal (grey line; D H was 1.48). (c) Analogous to (a), but for the difficult task one-footed stand with closed eyes (OFCE) which is associated with large elongations. SD was 8.82 mm (SD of noise was 0.05 mm) resulting in a SNR of 176.4. (d) Analogously to (b), but for the signal shown in (c). D H ranged from 1.03 to 1.08 and was 1.06 for the entire time signal.

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