Hi Kevin and Jiansong,
> One more question: How can I set contrast so that the motion parameters are
> calculated into the result SPM{T} images?
as this is along the same lines as Kevin's question, I take the liberty
of answering both in one go: you don't need to set up a contrast in
order to have the effect removed from the session (or say, at least
taken into account). Since the parameters were entered as covariates,
the statistics is assigning to them "activation" in the images (ie,
motion effects) explainable by them. This is wholly independent from
whether you ever look at the contrast or not. Try it: make 2 one-session
models, once with, once without motion parameters, and compare the
t-images or your contrast of interest. They will be different.
Also, it does not really make sense to look at the effect of one
parameter since it will likely covary with the other ones (ie, motion in
X will covary with, say, pitch). You could enter 0 0 1 1 1 1 1 1 for a
session with 2 conditions and 6 motion parameters to see the effect of
motion, if you wanted to. It is not likely to be meaningful in many way,
though :)
One interesting question, though, is whether one should orthogonalize
the motion parameters wrt the contrast of interest ? I have thought
about this but as usual did not come up with a good answer since there
seem to be arguments in favor and against doing so (again, as usual :) I
would like to hear the real expert's opinion on this.
> your help are highly appreciated
I am ever so happy to be of help :) Seriously, what I know about spm I
have mainly learned from this list and its fabulous contributors, and I
think we should all keep it going as strong as we can (now here's a
motto for the day :)
Best,
Marko
--
=====================================================================
Marko Wilke (Dr.med./M.D.)
[log in to unmask]
Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
=====================================================================
|