About my previous post,
I believe that performing PPI on orthogonalized modulators should make sense.
The rationale is to test brain voxels that correlate with activity in one VOI, as a function of its interaction with aspects of a parametric modulator that cannot be accounted for by other regressors.
However, I would like to have the opinion of some expert on both PPI and pmod (e.g., Donald McLaren).
Best,
David
|