HAPPY ENDING, RICK!!!
Turns out all John needed to do was "split" the 4D NIFTI file into 528 3D files (i.e., one for each volume), then loop them through his normalization command. After this step, the (normalized) 3D files were put back together into a 4D file.
Only one slight problem remains. For some reason, in the header of this newly reconstructed 4D file, the TR is listed as 1 second. (Perhaps this is a default setting?) So Rick, given that I used a 2-second TR for my fMRI study, is it possible to overwrite this info?
Thank you!
Most gratefully yours,
Whitney