I am somewhat new to SPM and am interested in group differences, but do not
fully understand this reply. What does "Each subject gets a separate
session, in which you model condition A." mean? Does this mean you have to
compute the A-B contrast image for each individual first and then input
each of those 20 images into the new model?
Thanks for you help,
Vicky Morgan
Victoria Morgan, Ph.D.
Department of Radiology
Vanderbilt University Medical Center
Nashville, TN
On Fri, 30 Jun 2000 18:40:48 +0100, Stefan Kiebel
<[log in to unmask]> wrote:
>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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