Reply-To: | | [log in to unmask][log in to unmask]> >>>>>>> wrote: >>>>>>>> Hi all, >>>>>>>> I have a question concerning the code used to implement a PPI analysis. >>>>>>>> >>>>>>>> In the spm_peb_ppi.m function packaged with SPM8, lines 329-332 remove >>>>>>>> confounds from the input seed region¹s time course: >>>>>>>> >>>>>>>> % Remove confounds and save Y in ouput structure >>>>>>>> %---------------------------------------------------------------------- >>>>>>>> -- >>>>>>>> -- >>>>>>>> Yc = Y - X0*inv(X0'*X0)*X0'*Y; >>>>>>>> PPI.Y = Yc(:,1); >>>>>>>> >>>>>>>> PPI.Y is then to be used as a covariate of no interest when building >>>>>>>> the >>>>>>>> PPI >>>>>>>> regression model. However, on line 488, it is the uncorrected seed time >>>>>>>> course, Y, that is input to the deconvolution routine and used to >>>>>>>> generate >>>>>>>> the ppi term: >>>>>>>> >>>>>>>> C = spm_PEB(Y,P); >>>>>>>> xn = xb*C{2}.E(1:N); >>>>>>>> xn = spm_detrend(xn); >>>>>>>> >>>>>>>> % Setup psychological variable from inputs and contast weights >>>>>>>> >>>>>>>> %---------------------------------------------------------------------- >>>>>>>> PSY = zeros(N*NT,1); >>>>>>>> for i = 1:size(U.u,2) >>>>>>>> PSY = PSY + full(U.u(:,i)*U.w(:,i)); >>>>>>>> end >>>>>>>> % PSY = spm_detrend(PSY); <- removed centering of psych variable >>>>>>>> % prior to multiplication witk†
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