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We are working on a manuscript revision for an fMRI project that was analyzed with FS-FAST 5.3 years ago. We used mri_glmfit, and then we ran mri_surfcluster (instead of mri_glmfit-sim) with a vertex-wise threshold of p<0.001 and a cluster threshold of 100mm^2. We had applied 8 mm smoothing at the group-level, and the voxel size was 3.125x3.125x5 (resampled to fsaverage surface and to MNI305).
1. One reviewer asked us to provide a rough estimate of the family-wise error rate (FWER) that a cluster threshold of 100mm^2 is equivalent to, or alternatively, to re-analyze everything with mri_glmfit-sim permutation. It would be simpler to provide the FWER estimate. To get the FWER estimate, we referred to Woo et al (2014). However, their simulations were for volume analyses, not surface analyses. What is the FWER (roughly) for a primary threshold of p<0.001 and cluster threshold of 100mm^2? (Obviously, we are hoping for a number less than 0.05.)
2. For the volume, we used mri_surfcluster with a primary (voxel-wise) threshold of 0.001 and a size threshold of 300mm^3. If I’m understanding correctly, Figure 2 from Woo et al. (2014) suggests a FWER p<0.05 might roughly correspond to a cluster size threshold of 200 to 985 voxels (1600 to 7880 mm^3), depending on intrinsic smoothness. That would likely put our threshold of 300mm^3 well above p<0.05. Is this correct?
Thanks,
-Kayle