> I want a statistical brain map that contrasts Root_effect with Sem_effect.
> How do I achieve that?
That kind of comparisons is not available in 3dMVM because such a comparison is not always meaningful in general; for example, two such variables may have different metric (e.g., height and weight), therefore their comparison would be uninterpretable.
What is the underlying logic for such comparisons in your case?
Gang