Dear Olga,
> I realize that a beta or a con for 1 time bin are equivalent, but I was looking at how to export several time bins to the rfx simultaneously. What I was aiming at doing was to compare the HDresponses (corresponding 14sec windows) for the 2 groups, so would it be correct to create a con image at the individual level: 11111111-1-1-1-1-1-1-1 and then export those to the 2nd level? Ideally, the best analysis would be a cross-correlation with sliding window but unfortunately I do not know of any way to do this in SPM. It seems that Brain Voyager has a feature that allows that, but I have not found anything equivalent in SPM. Do you? (or anyone else?)
Creating a con image looking at the difference of the first 7 bins and
second 7 bins is perfectly valid, and has the advantage of giving you
a single summary of activity for each subject, which makes the 2nd
level analyses simpler.
If you just want to identify any differences between groups, you could
set up an F test that would test for a difference at each of the bins.
But, this may be problematic when assessing the group effect (see
recent discussions on the list about validity of group comparisons in
2nd level models). So some summary measure which can be used in a
t-test is probably your best bet. (Which you could do on the contrast
you've specified, or any other similar summary contrast.)
[I think you mistyped above and have included all 15 bins, rather than
just 14; I think you meant: [ones(1,7) -1*ones(1,7)]. Just making
sure! :) ]
Best regards,
Jonathan
--
Dr. Jonathan Peelle
Department of Neurology
University of Pennsylvania
3 West Gates
3400 Spruce Street
Philadelphia, PA 19104
USA
http://jonathanpeelle.net/
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