Fig. 4.
Spatial in homogeneity of εHF values is illustrated through a histogram (A), an axial (X= − 2) (B), a sagittal (Y = 36) (C) and a coronal (Z = 27) view (D) at 5192 voxels (resolution: 3.5 × 3.5 × 3.5 mm3) that reached the significance level of 0.05 for UVT-UC. Cell width in (A) is 0.01. The distribution of εGG (not shown here) is similar. Notice that 1/9 ≤ εGG ≤ εHF ≤ 1 (Appendix D), mean(εGG) = 0.439, sd (εGG) = 0.105, mean (εHF) = 0.488, sd(εHF) = 0.130. Coronal view (D) and the colored clusters are the same as in Fig. 3A. Red, green and blue in (B) and (C) correspond to no, mild, and severe violation of sphericity assumption. A substantial amount of variability in εHF exists within and across brain regions; that is, the severity of sphericity violation is spatially heterogeneous.