Hi Tibor
> Dear SPMers,
> I have a question, wich may be basical, but I have not found an answer
> in some papers I have investigated yet.
sure you can found some stuffs about that ...
> We have made a group comparison with SPM5 by using the twotimes six
> fMRI-measurements as twelve and appyling a design matrix
> "1 1 1 1 1 1 -1 -1 -1 -1 -1 -1"
> (1-6: first session, 7-12: second session)
> I hope it is correct (according to manuals)
> We have got some result which means there are some areas with positive
> alteration.
well what you have is a 'stronger' activation for the 1st session than
the 2nd one
> The question is that, how can it be determined, whether it is higher
> activation or smaller deactivation (both are positive changes).
> I have read same papers but neither of them took care of this problem.
some people do :-) the problem is obviously the baseline .. a
positive change can be in comparison with the mean signal overall brain
or with a control or baseline (rest) condition .. anyway you are right
to look at these effects. What you have to do is to look at the effect
of each factor with a F doing [1 1 1 1 1 1 ; 0 0 0 0 0 0 1 1 1 1 1 1]
(in this case there is no control condition) then plot this F contrast
in the area(s) showing the effect you are investigating (i.e. for the
contrast 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1). Then you can check that both
are positive, i.e. session 1 > session 2, or both negative, i.e. session
1 less deactivated than session 2 or session 1 positive and session 2
negative .. for more information on this see
*Gusnard, D. A. and M. E. Raichle (2001). *Searching for a baseline:
functional imaging and the resting human brain. /Nature Neuroscience 2:
685-694./
> Could somebody help?
hope I did
Best
Cyril
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