Analysis of the EEG Rhythms Based on the Empirical Mode Decomposition During Motor Imagery When Using a Lower-Limb Exoskeleton. A Case Study

Figures

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  Figure 1. Image of a subject executing one of the experimental trials.

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  Figure 2. Example of trial: (A) Details of the activation command. (B) Details of the MI tasks ~20 s (red) and relaxed state event ~10 + 10 s (blue), and moving reverse count (black top).

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  Figure 3. Empirical mode decomposition of one of the trials of subject S2 for Cz electrode. MI periods appear in red and relaxed state periods in blue. Each of the modes corresponds to the local oscillations of the signal in descendent value of frequency.

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  Figure 4. Instantaneous frequency of the first 5 IMFs obtained by EMD of one of the trials of subject S2. Each IMF oscillates within the EEG rhythms: IMF1 (Gamma), IMF2 (Beta), IMF3 (Alpha), IMF4 (Theta), and IMF5 (Delta).

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  Figure 5. Boxplot of the variation of power of the MI tasks related to the relaxed state: (A) Left image shows the variation of power for the nine electrodes averaged through the 10 trials placed in the motor cortex zone. (B) Left one shows it for the electrode Cz for the individual 10 single trials.

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  Figure 6. Instantaneous power of IMF3 after the acoustic cue for MI (black line) for trial 1 of subject S1. The value is compared with the instantaneous power of the signal filtered by a Butterworth filter (5–15 Hz). The peak response is higher using the IMF. REX start of movement is represented by a red spot.

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  Figure 7. Evolution of the instantaneous power for trial 1 of subject S2: (A) IMF1. (B) IMF2.