For time-frequency presentations and statistical analyses, the average PC of each of three midline electrodes (Fz, Cz, and Pz) relative to 18 other electrodes was computed (for example, Fz to Fp1, Fp2, F7, F3, F4, …, O2; Cz to Fp1, Fp2, F7, F3, Fz, F4, …, O2, etc.). These average PC values in each frequency bin and time lag were then averaged across subjects (grand averages) and displayed in corresponding time-frequency diagrams. In addition to this “integral measure”, we analyzed also 9 pairs of interest that are most representative of connections within the left (F3-C3, C3-P3, F3-P3) and the right (F4-C4, C4-P4, F4-P4) hemispheres, as well as between the two hemispheres (F3-F4, C3-C4, P3-P4). For time-frequency representation, PLI values in each frequency bin and time lag were averaged across subjects (grand averages) and cortical sites: frontal (F7, F3, Fz, F4, F8), central (T7, C3, Cz, C4, T8), and parietal (P7, P3, Pz, P4, P8), and were then displayed in corresponding time-frequency diagrams. All analyses were carried out with an about equal number of trials (≥30) for different stimulus conditions.
