spatial anisotropic exponential (EXPA) matrix was used to model within subject covariance structure of the data. A scatter plot of the N2 peak amplitude and latency values with age showed a curvilinear trend, which was consistent with the observations of previous studies (Amenedo and Diaz, 1998; Czigler et al., 1997; Pekkonen et al., 1996; van der Stelt et al., 1998). Therefore, to model the linear and quadratic relationship, both age and age2 were included as fixed factors. A backward stepwise method was used to remove nonsignificant effects. Further exploration of main and interaction effects were performed using Wald's tests (Kenward and Roger, 1997) for pairwise comparisons and the significance levels were adjusted with Bonferroni correction for multiple comparisons. The demographic and behavioral data (i.e., age, education, MMSE score, reaction time, and error responses) were analyzed using t-tests.
