Wavelet packet-based independent component analysis for feature extraction from motor imagery EEG of complex movements

OBJECTIVE The main goal of this study was to develop a novel spatial filtering method for better extracting the feature information underlying the event-related de-synchronisation and synchronisation (ERD/ERS) during complex motor imagery of lower limb action. METHODS The algorithm used a wavelet packet-based independent component analysis (WPICA) method to extract the ERD/ERS patterns in different frequency bands. Time-frequency decomposition in the wavelet packet domain was designed to avoid the statistical correlation between different electroencephalographic (EEG) rhythms. The subband-specific principal components were extracted after independent component analysis and projected back to the time-frequency domain of corresponding electrodes for better fitting the varying EEG spatial distributions. RESULTS The present method was tested with the EEG data from 10 human subjects performing three complex mental tasks (i.e., imagery standing up, imagery left/right foot movement combined with homolateral hand movement). A classification rate of about 80% was achieved using the WPICA-based technique, which is better than the traditional ICA method with the rate of 72.30% and the non-spatial filtering condition of 68.34%. CONCLUSIONS We developed a novel spatial filtering method based on WPICA to extract the ERD/ERS patterns in different frequency bands. The overall performance of this algorithm was better than that of the conventional methods. SIGNIFICANCE The current method promised to provide an effective way for ERD/ERS patterns recognition and thus could improve the pattern classification performance of complex mental tasks from scalp EEGs.

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