Spatial Directionality Found in Frontal-Parietal Attentional Networks

Table 2

Signal processing procedure.

Steps	Description
(1) Data Preprocessing	Low-pass filter – Focus on frequencies below 40Hz.
(2) Signal Decomposition	Fast Fourier Transform – Extract real and imaginary parts of the signal.
(3) Electrode Pair Selection	Magnitude squared coherence is initially performed on electrode pairs considered to have significant coherence (> 0.6) for selection
(4) Unwrap Phase Function	The “unwrap” phase function is applied in order to return the phase angles in radians
(5) Mean and standard deviation calculation	For all the channels, the mean and the standard deviation were calculated.
(6) Directionality property analysis	Directionality is determined by the slope of mean of the unwrapped phases, which is either positive or negative, thereby constituting phase lead or phase lag. Phase directionality is designated as phase leads of the unwrapped phases between channels. Slope values are plotted to determine phase directionality in reference to each channel.