There's probably nothing messed up with the analysis, but it is worth
noting that the blob is not significant (unless you had some prior
hypothesis about this region).  It could easily be obtained just by
chance, as it does not really survive the correction for multiple
comparisons.

Best regards,
-John

-----Original Message-----
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of Sophie Josee Lafaille
Sent: Friday, January 26, 2007 7:01 PM
To: [log in to unmask]
Subject: [SPM] VBM spm5 Absolute threshold and white matter activation

Greetings fellow SPM'ers.

I am running a VBM analysis with 16 scans in each group, 2 groups.

I have looked at all the smwc1*.img files to make sure that they look
ok and are all properly registered.

using the specify 2-nd level analysis

I run a 2  sample t-test
use TIV as a covariate (calculated from get_totals)
use an absolute threshold of 0.05

and leave all the rest as defaults.

when looking at my patients>controls (-1 1), we find a small cluster
in the right temporal lobe, see attached.

after mni2tal transform and lookup in atlas the peak of this cluster
(and indeed the majority of this cluster, %90) is located in white
matter.

I do realize that smoothing has a tendancy to shift clusters, but this
seems like a very radical shift.

does anyone have any ideas on how I might have messed up this analysis?

Thanks, and have a great weekend,

sophie



Sophie Lafaille, B.Sc.(Hons.), M.Sc.
Research Officer II, Speech Fluency Laboratory 1059
Graduate Department of Speech-Language Pathology
500 University Avenue, Toronto, Ontario, Canada M5G 1V7
Ph. 1-(416)-946-8635      Fax 1-(416)-978-1596
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