This paper may help explain what's going on:
Gerard R. Ridgway, Vladimir Litvak, Guillaume Flandin, Karl J.
Friston, Will D. Penny.
The problem of low variance voxels in statistical parametric mapping;
a new hat avoids a ‘haircut’. NeuroImage, Volume 59, Issue 3, 1
February 2012, Pages 2131-2141
Fred Bookstein's criticisms of VBM (also in NeuroImage) also covered
this, although it is a bit less straightforward to follow.
For this reason, I'd suggest making sure your GM mask extends far enough.
Best regards,
-John
On 1 April 2012 21:31, Valentino Pironti <[log in to unmask]> wrote:
> Dear All,
> I have done some VBM analyses with SPM5. The t test results are funny. Scattered blobs far outside the brain. I am aware it might be common but I checked t1 and segmented images, one by one, and excluded those that looked dodgy. However the problem persists. Any idea why is the problem still there?
> Thank you in advance for your help.
> Best
> Valentino
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