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Hi Lydia, As you have 2 conditions + baseline, sPPI is no longer valid. You should use gPPI. Best Regards, Donald McLaren, PhD On Sat, Mar 9, 2019 at 12:37 PM Philipp Kuhnke <[log in to unmask]> wrote: > Hi Lydia, > > ah I see! You seem to be talking about the PPI GUI tool in SPM, which > implements "standard" PPI (sPPI). I always conduct my PPI analyses using > the generalized PPI (gPPI) toolbox: https://www.nitrc.org/projects/gppi > So I'm afraid I can't answer this question and need to refer to the SPM > experts. > > However, I can highly recommend gPPI as it generalizes PPI to experimental > designs with more than 2 conditions - in these cases, sPPI is no longer > valid. See: https://www.ncbi.nlm.nih.gov/pubmed/22484411 > I am not sure whether sPPI is valid for your design with 2 tasks + a > baseline condition. Maybe a PPI expert like Donald McLaren can help here. > > The VOI timecourse extraction itself should not depend on any contrast; > it's simply the raw timecourse of the voxels (or more precisely, usually > the first eigenvariate of the BOLD signal from the voxels), possibly > adjusted for effects of interest (but this is chosen elsewhere). > > All the best, > Phil >