Dear Experts,
I am a relatively new user of SPM and have been unable to find a clear answer to the question of what is contained in the SPM.xVol.FWHM file. I would like to obtain the intrinsic smoothness of the data (not the statistical map) to feed into 3dClustSim of the AFNI package. I know for AFNI users, this is usually the output of 3dFWHMx, which gives the average smoothness of the residual time series across all participants. When I look at the SPM.xVol.FWHM at the group-level for a specific contrast, is this number the SPM equivalent to AFNI's FWHM output? If not, what exactly do the numbers in the file represent? I tried running 3dFWHMx on each type of map (con, spmT, ResMS) and was not able to replicate the values contained in xVol.FWHM.
Any help you can provide is highly appreciated!
Umi
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