Hi Christophe,
> FWE correction with the GFT does NOT only rely on the volume
> (i.e. voxel count) but also on the shape of this volume.
Interesting point... this isn't actually the case normally, because
SPM just uses a single global resels-per-voxel estimate in combination
with the number of voxels in order to decide how many resels there are.
You're right that small volume correction (SVC) does take the shape
into account, but only if you specifically request SVC. Most people
only do this if they are using small ROIs -- I guess arguably it
should always be used, especially if the masking is quite severe (I've
seen absolute thresholds of 0.2 advocated on this list for VBM, which,
at least on my data, gives a very tight mask).
What do other people think about this? Should tight/convoluted GM
masks be treated with SVC like small ROIs are, or is there a good
reason why not?
Best,
Ged.
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