previous post, the center voxel is black, the one-voxel radius surrounds red, and the two-voxel radius surrounds purple.
This two-voxel radius searchlight has 13 + 21 + 24 + 21 + 13 = 92 voxels in the surround, which makes it larger than the three-voxel radius faces-must-touch searchlight (at 86 surrounding voxels).
So how should we grow searchlights, edge-face-corner, edge-face, faces-only? Beats me. I can imaging comparing the results of a few different shapes in a particular dataset, but I doubt there's a single shape that is always best. But the searchlight shape should be added to our list of how to describe a searchlight analysis.
PS - I use R code to generate lists of adjacent voxels for running searchlight analyses; contact me if you'd like a copy/details.