afni.nimh.nih.gov

> I've tried to include the same vVar file across both levels of Valence now so that there are not two levels.

If you want to use the difference score as a covariate, then you would also need to do the same for the conditions: use the contrast between the two conditions as input. That is, variable "Valence" would disappear from the model. And 3dttest++ would be good enough.

Gang