Group Average Parietal Potentials. Group average (n = 8) bar graphs for parietal potentials (A) N20, (B) P27 and (C) P50 as recorded from electrode site(s) CP3/4. Amplitudes are expressed relative to control values. For bar graphs A & B, (ND) non-dominant hand movement; (D) dominant hand movement. White bars represent group data from the right hand dominant group; black bars represent group data from the left hand dominant group. P50 amplitudes (C) are collapsed across handedness and represent amplitude for timing epochs Early Bereitschaftspotential (EBP); Late Bereitschaftspotential (LBP); Movement (MVMT); Post-Movement (PMVMT). Error bars are ± SEM. * denotes significance p < 0.05.