Reply-To: | | [log in to unmask][log in to unmask]> >>>>> wrote: >>>>>> Hi Donald, >>>>>> As far as I can tell, spm_regions filters and whitens the VOI time >>>>>> series, >>>>>> and adjusts for the null space of the contrast if an adjustment is >>>>>> specified >>>>>> in xY.Ic. It defines the confound matrix, X0, but does not correct for >>>>>> it. >>>>>> The following line in spm_peb_ppi corrects for the confounds. >>>>>> >>>>>> Yc = Y - X0*inv(X0'*X0)*X0'*Y; >>>>>> PPI.Y = Yc(:,1); >>>>>> >>>>>> So the above correction does seem to be doing something different to >>>>>> spm_regions. I'm wondering why the uncorrected data, Y, is used when >>>>>> generating the ppi interaction term, while the corrected data Yc is to be >>>>>> used as a covariate of no interest in the PPI model. I would has thought >>>>>> that Yc should be used to generate the ppi interaction term as well. >>>>>> >>>>>> In my data, my X0 is a 195 x 7 matrix (I have 195 volumes per session). >>>>>> >>>>>> Regards, >>>>>> Alex >>>>>> >>>>>> >>>>>> On 30/04/2011 02:22, "MCLAREN, Donald" <[log in to unmask]> wrote: >>>>>> >>>>>>> I'm actually travelling at the moment. However, I know Y has already >>>>>>> been adjusted as part of the VOI processing. >>>>>>> >>>>>>> Can you check what X0 looks like? >>>>&Õ³;•g |