I've just started to learn DCM and I was wondering what would be the best way to specify my model.
My experimental design consists of a 2 condition x 3 valence. Condition has two levels (active and passive), and valence has three levels (positive, negative and neutral). The example in the SPM manual uses a visual input regressor consisting of every visual stimulus, but this doesn't seem to be the recommendation for factorial designs, so I'm wondering how to use the SPM design I already specified.
My hypothesis is that there will be forward connectivity from region A to region B for positive emotional words only in active condition but not in passive condition. So is condition my modulatory input and all words my driving input? Or should I specify only positive words as my driving input?
In the SPM design matrix I have the following regressors
ActivePos, ActiveNeg, ActiveNeu, PassivePos, PassiveNeg, PassiveNeu
With only two regions, and the driving input to region A, my C-matrix should look like 1 1 1 1 1 1; 0 0 0 0 0 0, correct?
If active condition has a modulatory effect on connection A to B during positive words, then my B-matrix should be
is that correct?