The spatial extents of differential activation (“Incongruent – Congruent”) in the whole-brain within-group analyses shown through color maps (voxel base p value ≤ 0.005 and whole-brain corrected p value ≤ 0.021, red or orange = IC is more active than C, and blue = C is more active than IC.) for (a) young adults' successful trials, (b) older adults' successful trials, and (c) older adults' successful and error trials together. The cross hair indicates the existence of the L SFG cluster in (c) but not in (b). The contrast of error IC versus successful C trials at voxel base p value ≤ 0.005 (not whole-brain corrected, but with cluster size ≥ 150 mm3) is shown for the sub-group of nine older adults who made reasonable number of IC and C errors (d). Some key active regions are indicated. IC = Incongruent, C = Congruent, R = right, L = left, IFG = inferior frontal gyrus, MFG = middle frontal gyrus, PCG = precentral gyrus, and BA = Brodmann area.