Table 3 shows the correlations among the latency and amplitude measures for the target and rare non-target conditions. The four latency measures were highly correlated with each other with between 25 and 38% of the variance being shared between measures. The P3a and P3b amplitudes were also highly correlated, as were the N2a and N2a amplitude, but the P3 amplitudes were not correlated with the N2 amplitudes. The lack of association between P3 and N2 amplitudes suggests that the group effects on these measures likely are independent of each other. Nonetheless, analyses of covariance were carried out to determine whether the P3 and N2 group effects characterized overlapping variance (i.e., using one variable as the dependent variable and the other as the covariate). The first analyses showed that the N2b amplitude difference between groups was independent of the P3b amplitude difference. The group effect went from accounting for 6.3% to 5.3% of N2 variance when P3 amplitude was entered as a predictor. The N2 group effect was still significant (F(1, 132) = 7.42, p = 0.007), while P3 amplitude did
