Figure 1.

Representative voxel illustrating testing of the null hypothesis (H₀ : $m=1$). To assess whether the null hypothesis is true in any given voxel, a t-test comparison of the $\alpha$ and $\beta$ residual values was used. When $\alpha \hspace{0.17em}\ne \hspace{0.17em}\beta$, then the line was not significantly close to one and the voxel was considered to have a significant deviant slope. If the T value survived the correction for multiple comparison (3 contiguous voxels where FWE $P$ < 0.05), the respective brain area was considered to be a loci for general cognitive slowing. A second analysis is needed to identify areas where voxels with slopes of −1 were eliminated in the residual analysis.