Dear everyone,
I think the uncorrected cluster p values always refer to properties of the whole brain analysis. If your VOI cuts off some parts of a cluster from the whole-brain analysis then the uncorrected cluster p value in the results table is altered, but this new uncorrected cluster p value is identical to the uncorrected cluster p value of another cluster with the same extent in the original whole-brain analysis.
In contrast, FWE-corrected cluster p values are adjusted depending on size of the VOI and properties of the VOI (sphere, box, or image, they result in different calculations).
Thus, corrected cluster p values can indeed become smaller than uncorrected ones.
Best
Helmut
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