I have to admit, I believe I solved this very problem 5 to 8 years ago, but I think I forced the solution. Anyhow, what I want to do is correlate (ala 3dttest+++) a psychological score with cortical thickness across 50 subjects and obtain a group .gii or .nii or whatever group file that I can then threshold and find ROIs from the cortical thickness analysis. I have done this with FreeSurfer, but as I remember their parcellation can issues with significant clusters that happen to cross over parcel boundaries.
My specific question is: What files from SUMA make spec process (which made the folder and contents in the attached .png) would I use for a basic cortical thickness mass univariate correlation analysis? What would the subject files be and are there different levels of smoothing, etc in the files made by SUMA Make Spec process? Does anyone have any suggestions? The files made by that command are rather opaque, am I not finding a basic primer on SUMA?