Yeah, well I was confused about this too, but I think it is in fact surface data, despite the .mgh suffix. I base that mainly on the fact that I can open the .mgh file as an overlay in tksurfer, but not in tkmedit. I also tried Nick's method of converting to NIFTI using mri_convert, but was unable to produce a NIFTI file that AFNI could open. I did manage to produce a .1D file that I could view in SUMA, and that appears to be in registration with the surface, by using the following steps:

1) mris_convert -f ${a}.mgh rh.white ${b}.gii
2) gifti_tool -infile ${b}.gii -write_1D ${c}.1D

I am definitively not FreeSurfer wiz, and their approach to documentation appears slightly different from AFNIs, so I would appreciate some feedback on what I am doing here. But like I said, for now it produces a file that looks correct, when viewed in SUMA.

If anyone is interested, the data were from the anatomical retinotopy template, created by Benson and colleagues.

Best,

Peter