Laura,
Laura Mancini wrote:
>Dear SPMers,
>
>I was wandering if you could help me understanding the following about SPM
>for fMRI data analysis.
>
>Once the fMRI anlysis has been performed to represents the results, in my
>understanding, it is needed to choose a (t or F) contrast, chose between FWE
>and FDR, choose a threshold, and the results are dispayed.
>If there is only one condition compared to rest and the contrast is +1 0,
>then the activation is shown.
>
This is true for a t contrast. An F [1 0]' contrast will show both
estimated activation and deactivation at the same map.
>But if the contrast is -1 0, does it show the
>
>
>regions with de-activation?
>
>
Again, that is true for a T contrast. An F contrast [-1 0]' is
equivalent to an [1 0]' contrast.
>And if one has got more than one condition and wants to compare them, for
>example one wants to subtract the activation due to one task from the
>activation due to the second task, how do the contrasts need to be chosen?
>
>
If you want to compare conditions I'd give a look at recent posts like http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0503&L=spm&P=R42379&I=-3&m=11463
for a start. Then maybe you can give a look at the chapter referenced in that mail. If you want to compare Cond1 and Cond2, i.e Cond1>Cond2, then a T [1 -1]' contrast would be ok (supposing Cond1 is the first column, Cond2 the second one, in your design matrix).
Hope this helps,
Juan J.
>Many thanks,
> Laura
>
>
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--
________________________________________________________
Juan José Lull Noguera - jualulno_at_upvnet.upv.es
[MI - Medical Imaging Area]
BET - Bioengineering, Electronics and Telemedicine Group
UPV - Politechnical University of Valencia - Spain
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