Hi Anita,

The subject movement during the EPI scan does not really apply
to that option. The -big_move option is useful when the
alignment between the EPI base and the anatomical image is not
fairly close to begin with. There is also a -giant_move option
that uses a bigger search space.

I am not positive what -big_move actually does, but it may be
to align the centers of mass, first. That would start with
the volumes in basically the same location before attempting
registration. Maybe Daniel will correct me if I'm wrong.

This might be useful if the subject moved far between the EPI
and anat acqusitions, or if they left the scanner, or if your
data format does not contain all of the location information,
etc. It's hard to guess.

In any case, -big_move has little to do with the motion
parameters in EPI registration.

- rick