Hi Lzy,
Yes, 0.3 is the default used by uber_subject.py when
creating an afni_proc.py command (afni_proc.py has no
direct default). That seems to be a reasonable default
for healthy human adults.
The unit is almost mm, in that it equates degrees with
mm (which seems fair, since a 1 deg rotation will move
a point most of the way to the surface about 1 mm).
So using 0.3 would make the per-TR censoring threshold
0.3 mm (not 3 mm).
- rick