Wavelet entropy in event-related potentials: a new method shows ordering of EEG oscillations

In this work we show the application of a measure of entropy defined from t he wavelet transform, namely the wavelet entropy (WS), to the study of even t-related potentials (ERPs). WS was computed for ERPs recorded from nine he althy subjects with three different types of stimuli, among them target sti muli in a cognitive task. A significant decrease of entropy was correlated with the responses to target stimuli (P300), thus showing that these respon ses correspond to a more "ordered" state than the spontaneous EEG. Furtherm ore, we propose the WS as a quantitative measure for such transitions betwe en EEG ("disordered state") and ERP ("ordered state").