[Freesurfer] cluster including vertices below cluster-forming threshold

Dear all,

I have some questions about the outputs of mri_glmfit-sim (which I used to perform permutation tests on my surface analyses).

When I compare *.sig.clusters.mgh and *.sig.masked.mgh surfaces, I notice that the clusters reported as statistically significant also include some vertices that are slightly below the cluster-forming threshold (especially at the borders of the clusters). It would appear as if some spatial smoothing has occurred on the clusters themselves.

Why is it so? Is there a way to perform clustering on the data that are above cluster-forming threshold?

Thanks,

Marco

_____________________

Marco L. Loggia, PhD

Postdoctoral Fellow, Mass General Hospital & Brigham and Women's Hospital

Harvard Medical School

CNY Building 120, suite 101E

Charlestown, Massachusetts 02129

Phone: (617) 643-7267

Fax: (617) 643-7340 marco@nmr.mgh.harvard.edu