Ee 791 Eeg-6

Coherence and Phase Synchronization Spatial analysis of EEG means the analysis of a joint observation of time series {Vmk(t) consisting of k =1,K observations in m = 1, M data channels. Coherence between pairs of electrodes provides an entry point to examine the spatial properties of the stochastic source activity. Coherence is defined as a linear correlation coefficient that primarily estimates the amount of phase synchronization between any two data channels. Figure 99 shows 3 different examples of phase synchrony or otherwise between two sine waves with the same frequency. In (a) the sine waves have the same amplitude, phase and phase difference for each trial (a deterministic signal, coherence 1); (b) signals have variable phase between trials but always a 45 degree phase difference (coherent stochastic process, coherence 1); (c) variable phase and variable phase difference (incoherent stochastic process).