Optimized shift-invariant wavelet packet feature extraction for electroencephalographic evoked responses

Local discriminant bases (LDB) have a major disadvantage in their representation which is sensitive to signal translations. The discriminant features will be not consistent when the same but shifted signal is applied. Thus, to overcome this problem, an approximate shift-invariant features extraction based on local discriminant bases is introduced. This technique is based on approximate shift-invariant wavelet packed decomposition which integrate a cost function for decimation decision in each sub-band expansion. This technique gives a consistent best tree selection both in top-down and bottom-up search method. It also provides a consistent wavelet shape in a shape-adapted wavelet method to determine the best wavelet library for a particular signal. This method has an advantage especially in electroencephalographic (EEG) measurement in which there is an inter-individual shift in time for the signals. An application of this method is provided by the discrimination between signals with transcranial magnetic stimulation (TMS) and acoustic-somatosensory stimulation (ASS).