Time frequency characterization of evoked brain activity in multiple electrode recordings

This paper explores global time frequency approaches to EEG data analysis with the Wigner Distribution Function and the Symmetric Ambiguity Function. The task chosen was to characterize the activity profile of EEG signals in sample Frontal, Central and Occipital electrodes from human subjects, coincident with the perception of a reversal in the orientation of a bistable Necker cube figure. The result of this analysis has implications for blind signal processing as the goal was to identify an unknown input source eliciting the observed EEG signals. The methods demonstrate an internally initiated EEG signal source not tied to a regularly anticipated external source. The results demonstrate the general applicability of the methods for a wide variety of neural and biological signals and systems. The findings can be summarized as the observation of high energy activity patterns in terms of significant dissimilarities in the waveform, both in time and frequency, in the Frontal and Occipital electrodes, approximately 200-600 ms prior to the appearance of the premotor potentials in the medial electrodes. Index Terms--Ambiguity function diagrams, bistable images, EEG, time frequency analysis, Wigner distribution function.