The choice of a simple Σ structure here is to allow manageable number of simulations while in the same time providing a reasonable structure similar to the one adopted for the Gaussian prior in Marrelec et al. (2003) that guarantees the HDR smoothness. To explore the impact of sample size, the number of subjects in each group was simulated at n = 9, 12, 15, 18, 21, 24, 27, 30 with ρ = 0.3 for each of the six scenarios. The standard error σ varied (shown in Figure 1) across the scenarios to obtain comparable power for each n. 5000 datasets were simulated, each of which was analyzed through 3dMVM with two explanatory variables, Group (between-subjects factor with 2 levels) and Component (within-subject factor with 7 levels that are associated with the 7 basis functions). False positive rate (FPR) and power were assessed by counting the datasets with their respective F- or t-statistic surpassing the threshold corresponding to the nominal significance level of 0.05. Similarly, one- or two-sample t-test was performed on the AUC and L2D values respectively.