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Make sure that you delete any existing SPM.mat file in the directory. Sometimes SPM can get confused if one model requires Vi and another model doesn't. I've come across this a few times before and it has to do with the variance settings and SPM not being able to find the required elements. Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Postdoctoral Research Fellow, GRECC, Bedford VA Website: http://www.martinos.org/~mclaren 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. On Wed, Feb 27, 2013 at 8:34 PM, Jason Steffener <[log in to unmask]> wrote: > Bon jour Lucile, > Off the top of my head it sounds like you are doing a group analysis > but are using the within subject model specification. The within > subject analysis (first level) expects time series data and I am > pretty sure the Vi is the autocorrelation estimation part. So if you > use one image per subject to do a group analysis you need to use the > second level modeling and not the first level. Please make sure that > you are using second level modeling and if so, then I am wrong and am > sorry to waste your time. > > Best, > Jason > > > > On Wed, Feb 27, 2013 at 4:29 PM, Lucile Rapin <[log in to unmask]> wrote: >> Hi SPMers, >> >> I m occuring some trouble when i run a model estimation for a one-sample t test. It happens for 2 groups separately. >> This is what i get in Matlab: >> >> Initialising parameters : ...done >> Plane 46/46 , block 1/1 : ...done >> Temporal non-sphericity (over voxels) : ...ReML estimation >> Failed 'Model estimation' >> Reference to non-existent field 'Vi'. >> In file "/Applications/spm8/spm_spm.m" (v4191), function "spm_spm" at line 868. >> In file "/Applications/spm8/config/spm_run_fmri_est.m" (v4022), function "spm_run_fmri_est" at line 33. >> >> The following modules did not run: >> Failed: Model estimation >> >> On the odd part is that when i run two-sample t-test with these 2 groups involved, the model estimation runs fine. >> Can anyone help me understand the error and find a way to fix it? >> >> Thanks a lot, >> >> Lucile Rapin, Ph.D >> Post-Doctorate Researcher, >> UQAM