Hi Satoru,
> Use of cluster-extent test has been discouraged in VBM data analyses since
> the early days of VBM because of non-startionarity associated with warping
> during the spatial normalization process. To get around this problem, you
> have to measure the image smoothness locally at each voxel, then you have
> to adjust cluster extent based on this local smoothness measure. SPM
> produces an image called RPV.img (RESEL per voxel image) during an
> analysis, which can be considered as the measure of local "roughness" and
> can be used to adjust the cluster extent. The problem with RPV is that it
> has a lot of variability in it, since it's calculated at each voxel and not
> pooled over all the voxels. When you do a statistical inference, this
> variability in RPV needs to be accounted for, and reduces the sensitivity
> of the test quite a bit.
Thanks very much for this - it's very helpful. Do you have a view on
the extent of the problem if you simply assume that the image is
stationary, at 8mm, 12mm smoothing?
Best,
Matthew
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