Dear Federico,
Perhaps this will serve to encourage some more feedback...
>I am looking for an answer on the following matter.
>Small volume correction is applied when one has an a priori hypothesis on a
>particular region instead of the entire brain.
Actually. when one wishes to specifically ignore/deny all data outside the ROI(s)
and effectively pretend that your FOV only ever covered the ROI and nothing else.
Anyone disagree?
>The question is: what should one then do with the remaing brain bits ?
Simple: You either bury your head in the sand or include them in your ROI.
The next question begged is: How scientifically (not statistically) valid
is the ROI approach?
I suppose if you are not interested in 'activations' within eyeballs, earlobes
and nasal sinuses, using an ROI (which is what spm always does anyway
using mask.img) is fair enough, but how about CSF and white matter?
What sort of an 'extra comparisons price' are we currently paying for
better compliance with GFT assumptions?
More importantly, how meaningful is a fusiform gyrus or hippocampal
'ROI-activation' whilst in reality, there may be activations (or
artefacts) occuring all over the shop?
Regards,
Afraim
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Dr A Salek-Haddadi
Clinical Research Fellow
Institute of Neurology
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