Hi Rachel,
Perhaps this is a result of smoothing, after all, which has the effect of
'spreading' the activation. Even if the extracortical voxels are not
'activated' significantly in the individual functionals - the group analysis
may be sensitive to their raised activation due to the adjacent cortical
peaks. What smoothing kernel did you use?
Best wishes, Dirk
%%-----Original Message-----
%%From: SPM (Statistical Parametric Mapping)
%%[mailto:[log in to unmask]] On Behalf Of Rachel Holland
%%Sent: Wednesday, May 30, 2007 12:15 PM
%%To: [log in to unmask]
%%Subject: [SPM] RFX- compressed functional data
%%
%%Dear SPMers,
%%
%%I have a slight problem with a random-effects group analysis
%%and wonder if you might be able to help.
%%
%%Essentially my concern is that the group activations (as
%%shown by an SPMT image for one particular contrast) do not
%%line up with the outer edge of cortex in my averaged wmT1 or
%%the SPM single-subject canonical template.
%%This is the case for all group T images.
%%
%%Individual subject normalisation was accurate as verified
%%visually using check reg - both individual structural and
%%mean functional images match the T1 template and wmT1
%%accurately. The problem seems to arise when I do a group analysis.
%%
%%Is there a stage of processing I have done erroneously?
%%
%%Thank you in advance,
%%
%%Rachel
%%
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