Fig. 1.

The biasing effects of the vascular tree. Three-dimensional vector plot of the direction (colour map) and magnitude (length of arrow) of mislocalization at adequately sampled voxels within three representative planes (left axial, top coronal, bottom sagittal), based on a sample of 581 acute stroke lesions, normalized into standard stereotactic space and mirrored onto one hemisphere (see Mah et al., 2014 for details). The value at each voxel was calculated by labelling the stack of 581 lesioned volumes as being ‘affected’ or ‘unaffected’ depending on whether or not that voxel fell within the lesion in each volume, running a standard voxel-wise Fisher's exact test-based mass-univariate analysis on the two groups, and identifying the centre of mass of the resultant significant cluster, identified by the asymptotic p-value thresholded at a Bonferroni corrected p < 0.01. This procedure was performed at all voxels hit more than three times in the data set. Each arrow points from the true location of a voxel in the brain to the location where the mass-univariate model erroneously places it. The colour map corresponds to the orientation of this error vector in the visualised plane. Note that the mislocalization tends to follow the organisation of the vascular tree, with clusters corresponding to the branches of the middle cerebral, anterior cerebral, and posterior circulations. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)