Hi Jennine,
What does 3dinfo show for the output dataset?
Is the dataset identically zero?
If you add options "-debug 1" and "-dnode 36799",
you will get some information about what happens
with node 36799. This will include a 1dindex values
(showing what happens with some associated voxels).
You could then even add "-dvoxel VOX_INDEX", to get
info for any voxel, if you'd like.
These might give you a better idea of what is going on.
Your command looks fine to me.
Debug level 2 might show something useful, too.
- rick