[VoxBo] Area of activation expands after GLM

[Joonkoo Park]

Hi Dan,

I think it's the explicit smoothing causing expanded .prm.
I guess that's why there's a '-r or -s' options for vbsmooth.
Thanks for the explanation!

Joon


On 1/29/07, Daniel Y Kimberg <kimberg at mail.med.upenn.edu> wrote:
>
> Joon, hi.  The first thing I'd suggest is that you make sure you're
> looking at the same volume the GLM thought it was looking at.  In the
> GLM directory there should be a .sub file that lists the tes files.
> Those files should have a brain volume very similar to what's in the
> prm file (not exactly the same when there's head movement, since we
> use an intersection mask, but the prm should never include more voxels
> than you see in a given tes file).  If you look at the two and they
> still don't match, I'd suggest re-running just that GLM, in case there
> was some issue with multiple jobs working with the same files at the
> same time.
>
> Normally you tend to get this kind of effect with either explicit
> smoothing or the bit of smoothing that you get with resampling (e.g.,
> in realignment).  But the prm file mask should still generally
> resemble what you see in the tes files you're modeling, except when
> there's lots of head movement.
>
> > This is contrary to my understanding that glm calculation is voxel-based
> > and therefore the activation area should not be expanded or contracted.
> >
> > Am I missunderstanding here or is something wrong with my glm
> calculation (I
> > used vbmakeglm)?
> > Or is there something beyond?
>
> No, it's all voxel-based and the prm mask should be exactly the
> intersection mask of your tes files' masks.  If that's not the case,
> then something's gone wrong, probably something trivial (or you may be
> looking at the wrong tes files).
>
> dan
>
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