Dear Jerry,
I just saw that Sterling already answered, but I didn't want to throw
away my answer...
> I have two groups of fMRI subjects (10 young subjects and 10 old subjects). Both groups
> performed an AB block design where B was a control task. All data was spatially
> normalized. I have computed the effects of task A in each individual subject, and for
> the youngsters as a group, and for the oldsters as a group and for the total group.
>
> How do I determine regions that were significantly more active in the young group than
> in the old group (and vice versa).
I would put all subjects of both groups into one model. Each subject
gets a separate session, in which you model condition A. You can then
choose 2 contrasts to test young vs old. Given that you entered first
all young subjects, then all old subjects the contrast for testing,
where your young activate more than your old subjects would be:
1 1 1 1 1 1 1 1 1 1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
and old more than young:
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 1 1 1 1 1 1 1 1 1 1
You could also proceed to a 2nd level analysis. To do this you create
one contrast-image for each subject, where the appropriate contrast for
young subject #7 would be:
0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
You then enter the 20 images into a 2-sample t-test in 'Basic Models'.
Stefan
--
Stefan Kiebel
Functional Imaging Laboratory
Wellcome Dept. of Cognitive Neurology
12 Queen Square
WC1N 3BG London, UK
Tel.: +44-(0)20-7833-7478
FAX : -7813-1420
email: [log in to unmask]
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