> After thresholding and visualizing results, I extracted values of connectivity from clusters affected by the main effect
> and the reaction time (with 3dROIstats). But, in some cases, I DO NOT see correlations at all between reaction time
> and connectivity extracted from those clusters!
I assume that the clusters are selected from the statistically significant main effect of "reaction time". Sometimes it does happen that the voxel-wise result is not consistent with the result at the cluster level, and the inconsistency may have something to do with the averaging operation across the voxels within the cluster. Technically speaking, the two mathematical processes (computation of the statistic and averaging) are *not* commutative.
Gang