A time-frequency based bivariate synchrony measure for reducing volume conduction effects in EEG

Phase synchrony measures computed on electrophysiological signals play an important role in the assessment of cognitive and sensory processes. However, due to the effects of volume conduction false synchronization values may arise between time series. Measures such as the imaginary part of coherence (ImC), phase-lag index (PLI) and an enhanced version of it, the weighted PLI (WPLI) have been proposed in order to attenuate the effects of volume conduction. In this work, the computation of the WPLI based on the phase difference from the Reduced Interference Distribution-Rihaczek (RID-Rihaczek) time-frequency distribution is proposed. The proposed WPLI measure is shown to be less susceptible to volume conduction effects when compared to that based on phase difference estimates obtained from the continuous wavelet transform. The proposed measure has also been applied to real EEG data collected during a study of event-related negativity and has been shown to differentiate between real synchrony and synchrony due to volume conduction.