"I don't know if there are any standardized procedures for SVC."
I think the only paper published in a journal dealing with small volume correction or related procedures is by Friston (1997, Human Brain Mapping) "Testing for Anatomically Specified Regional Effects". However, at second sight, it actually seems to be rather different from the SVC nowadays. In Friston (1997) it works on the cluster ps, but the "search volume" is equivalent to the cluster.
Concerning the SVC in SPM, as far as I can see the correction is an approximation based on the proportion of voxels within the volume of interest relative to the voxels of the whole-brain volume, as the FWHM remains the same for SVC. However, the FWHM might be quite different in that particular volume of interest compared to the average value across the whole brain. Running a separate analysis with an explicit mask corresponding to the volume of interest, I obtained different FWHM, resel count, critical T and FWE corrected ps at least. This might have been influenced by other parameters though.
|