Hi Melanie,

Understanding why the mask extends so far out would require looking at
the EPI data. A mask that large is unusual in humans.

For details about masking, including why we do not suggest it at the
single subject level, look at the afni_proc.py -help output, and see the
section titled "MASKING NOTE" (there are lots of NOTE sections :).

To summarize, it makes some sense to decide explicitly what a good
group mask is, and to apply that in your group analysis command (e.g.
3dttest++), or even afterwards. This allows you to see all of the single
and group results, without masking away any issues that might be
useful to look into.

Masking at the group level also helps to avoid having partial data at
the edge voxels, which most of our programs are not prepared to handle
(i.e. degrees of freedom that vary across voxels).

- rick