just as an additional remark to Donald's advice, you of course will have
to normalize the images at some point in order to compare the subjects,
but with n = 8, you do not have enough subjects for a random effects
second level analysis. You could either perform a fixed effects analysis
similar to what you have tried before, but with limited
generalizability, or try a non-parametrical approach such as SnPM, which
will work with smaller groups. Alternatively, collect more data :)
Hope this helps,
MCLAREN, Donald wrote:
> You should only put in one subject to each SPM.mat file for the first
> level analysis. Then use the con_images in the second level analysis. In
> regards to your error, the images are not normalized to common space and
> as such, SPM is complaining.
> For each subject, you should do the following:
> (a) slice-timing correction (optional)
> (b) motion correction
> (c) normalization
> (d) smoothing
> These 3 or 4 steps will lead to all subjects being in the same common space.
> 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
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> On Fri, Mar 25, 2011 at 11:05 PM, Allison McMahon
> <[log in to unmask] <mailto:[log in to unmask]>> wrote:
> Hello. I am trying to perform a group analysis on eight subjects
> using SPM8. I am using the Specify 1st Level option. Attached are
> some screenshots of the analysis. I have performed this same
> analysis on eight separate subjects and I receive an SPM.mat.
> However, with the current group of eight subjects, I am receiving
> the following error:
> Failed: fMRI model specification
> I am trying to perform this analysis in order to find the activated
> voxels for the group.
> I would appreciate any help in resolving this issue.
PD Dr. med. Marko Wilke
Facharzt für Kinder- und Jugendmedizin
Leiter, Experimentelle Pädiatrische Neurobildgebung
Abt. III (Neuropädiatrie)
Marko Wilke, MD, PhD
Head, Experimental Pediatric Neuroimaging
University Children's Hospital
Dept. III (Pediatric Neurology)
D - 72076 Tübingen, Germany
Tel. +49 7071 29-83416
Fax +49 7071 29-5473
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