Fig 3. ERP waveform and topographic maps. Pannel A, B and C showed the ERP waveform maps on frontal (Fz, F1, F2), parietal (Pz, P1, P2) and occipital (Oz, O1, O2) electrodes, respectively. Pannel D indicated the topographic maps of the P1, P2, N2 and LPC.