Dear Guido,
> I would like to know how the mean adjusted data (y) of a selected voxel
> relates to the percent signal change that is almost always reported in
> publications. Is there a formula to compute % signal change from y?
>
> I extract the mean adjusted data for a particular voxel by averaging
> over a number of events from the "raw" data series (y) for that voxel.
I fear, that there is no good or standard answer on that, and there are always new discussions about that issue on the SPM list. Check the SPM archives
http://www.jiscmail.ac.uk/lists/spm.html
for getting a overview what the people are actually doing.
As a starter, you can look directly into
http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind04&L=SPM&P=R392137&I=-3
> As a second question: where do the extreme outliers in the adjusted data
> at the beginning of each session come from? Is there a way to avoid these
> outliers?
Have you made dummy scans or removed the first scans from the timeseries? If not, that's why you should always do that ...
Good luck,
Karsten
--
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Karsten Specht, PhD
Department of Biological and Medical Psychology
& National Competence Centre for functional MRI
University of Bergen
Jonas Lies vei 91
5009 Bergen
Norway
Tel.: +47-555-86279
Fax: +47-555-89872
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http://fmri.uib.no/
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