afni.nimh.nih.gov

> Did I understand correctly that a contrast like (Faces + Shapes) - Forms is not
> possible at the moment or did I specify it in a wrong way (see below).

Yes, you're correct. 3dLME can't handle this kind of contrasts right now. I would go with 3dMEMA for all of your tests, not just (Faces + Shapes) - Forms:

[afni.nimh.nih.gov]

Gang