Dear
SPMers
I've surfed the
spm-mailbase for some help on this but to no avail and would appreciate some
advice.
I have some fMRI
data that has 3 activation conditions and one rest
condition.
So, for the 4
conditions, (act1, act2, act3, Rest] I am aware that contrasts that are
specified of the form [1 -1 0 0] may be interpreted as both
increases in activity in act 1 versus act 2, or as decreases in act2 versus
act1.
If I am
principally interested in looking at increases in act1 versus act 2 [1 -1 0 0],
and not the decreases in act 2 versus act 1, would it make sense to
*exclusively* mask this contrast with the contrast designed to
explain reductions in act2 versus rest, i.e, [0 -1 0 1]? My
interpretation is that voxels that are common to both contrasts will be
excluded leaving voxel that are caused by an increase in activation of act 1
against act2. Is this correct?
Regards -
Mike
