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 region’s 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 with xn. Based on discussion with Karl >>>>>>> % and Donald McLaren. >>>>>>> >>>>>>> % Multiply psychological variable by neural signal >>>>>>> >>>>>>> %---------------------------------------------------------------------- >>>>>>> PSYxn = PSY.*xn; >>>>>>> >>>>>>> Is there any specific reason why Y, rather than Yc(:,1), is used to >>>>>>> compute >>>>>>> PSYxn? I thought Yc might be more appropriate (?). >>>>>>> Thanks for your help, >>>>>>> Alex >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> ------------------------------------------ >>>>>>> >>>>>>> Alex Fornito >>>>>>> Research Fellow >>>>>>> Melbourne Neuropsychiatry Centre >>>>>>> University of Melbourne >>>>>>> National Neuroscience Facility >>>>>>> Levels 1 & 2, Alan Gilbert Building >>>>>>> 161 Barry St >>>>>>> Carlton South 3053 >>>>>>> Victoria, Australia >>>>>>> >>>>>>> Email: [log in to unmask] >>>>>>> Phone: +61 3 8344 1876 >>>>>>> Fax: +61 3 9348 0469 >>>>>>> >>>>>>> >>>>>> >>>>> >>>>> >>>>> ------------------------------------------ >>>>> >>>>> Alex Fornito >>>>> Research Fellow<ùdeÃg |