Mean P300 amplitudes for positive and negative feedback for the three electrode sites (Fz, FCz, and Cz) are presented in Table 3. The grand averages for the two types of feedback at each electrode site are depicted in Fig. 5 and the topographical distribution of the current source density (CSD) of the P300 amplitude for each group and condition is displayed in Fig. 6. Repeated measures ANOVA conducted on peak P300 amplitude revealed significant main effects of feedback valence [F (1, 59) = 55.64, p < 0.001] and electrode site [F (2, 58) = 125.50, p < .001]. Post hoc tests revealed that P300 amplitude was larger in response to negative feedback (24.8 μV) than to positive feedback (18.6 μV). Furthermore, P300 amplitude was largest at FCz (24.3 μV) followed by the amplitude at Cz and Fz (23.1 μV and 17.7 μV, respectively). Table 3Mean and SD of P300 amplitude for the alcohol (n = 31) and placebo group (n = 30)FeedbackAlcohol groupPlacebo groupMeanSDMeanSDPositive Fz14.536.6314.987.75 FCz19.177.1820.248.47 Cz20.336.4022.207.62Negative Fz18.318.0022.809.30 FCz23.638.5929.3910.62 Cz24.488.3029.989.82
