Hi Rachel,
If that dataset is supposed to be in Talairach or MNI
space, then it is not properly constructed. The sform
code should be either 3 or 4 in that case, and then
AFNI would recognize it as such.
Supposing it is in MNI space. Fix the sform code using
nifti_tool, but note that such an operation requies an
uncompressed dataset. So:
gunzip dset.nii.gz
nifti_tool -mod_hdr -mod_field sform_code 4 -prefix dset_mni.nii -infiles dset.nii
Then you can run 3dmerge on the proper NIfTI dataset,
dset_mni.nii.
- rick