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? >>>>>> >>>>>> Best Regards, Donald McLaren >>>>>> ================= >>>>>> D.G. McLaren, Ph.D. >>>>>> Postdoctoral Research Fellow, GRECC, Bedford VA >>>>>> Research Fellow, Department of Neurology, Massachusetts General >>>>>> Hospital and Harvard Medical School >>>>>> Office: (773) 406-2464 >>>>>> ===================== >>>>>> This e-mail contains CONFIDENTIAL INFORMATION which may contain >>>>>> PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED >>>>>> and which is intended only for the use of the individual or entity >>>>>> named above. If the reader of the e-mail is not the intended recipient >>>>>> or the employee or agent responsible for delivering it to the intended >>>>>> recipient, you are hereby notified that you are in possession of >>>>>> confidential and privileged information. Any unauthorized use, >>>>>> disclosure, copying or the taking of any action in reliance on the >>>>>> contents of this information is strictly prohibited and may be >>>>>> unlawful. If you have received this e-mail unintentionally, please >>>>>> immediately notify the sender via telephone at (773) 406-2464 or >>>>>> email. >>>>>> >>>>>> >>>>&žð"g |