Thanks for this information. I went ahead and did that but I am still having difficulty getting the group analysis to recognize the GIFTI files - any thoughts?

1. Run conversion from .mgz to .gii
mris_convert -f taskBOLD_nBack_scan_8_lh.mgz $FREESURFER_HOME/subjects/fsaverage/surf/lh.white S1.l.func.gii

2. Use HCP pipeline to align to a standard mesh and merge hemispherse --> dscalar.nii file

3. Run 3dMVM which errors out:
*+ WARNING: NO spatial transform (neither qform nor sform), in NIfTI file 'SST_BOLD_S10_LR.dscalar.nii'
Then it says,

** Error:
Problem with input files! Two possibilities: 1) There is a specification error
with either file path or file name. Use shell command 'ls' on the last column in the
data table to find out the problem. 2) At least one of the input files has different
dimensions. Run "3dinfo -header_line -prefix -same_grid -n4 *.HEAD" in the directory
where the files are stored, and pinpoint out which file(s) is the trouble maker.
Replace *.HEAD with *.nii or something similar for other file formats.

4. 3dinfo -header specified no errors in dimensions between files

3dinfo -header_line -prefix -same_grid -n4 *.func.gii
prefix =grid? Ni Nj Nk Nv
S1.l.func.gii 1 10242 1 1 37
S2.l.func.gii 1 10242 1 1 31


5. Just using the .func.gii files and ignoring the steps to combine the hemispheres and align to a standard mesh, still produces an error stating that the file inputs are problematic.