Hi Robin,

That is right, we are not experts in SPM... :)

Indeed, the duration parameters are not allowed to be zero. Maybe just as a precaution, I'm not sure.

There is no difference between dmBLOCK with a 0.6 s event and BLOCK(0.6). There is a slight difference with BLOCK(0.6,1) in that is scales to unit height. Without that, a duration under 1s will tend to scale to a maximum of around that duration. So with a small duration, the ",1" is usually preferable.

But anyway, a small scalar effect will not alter any statistics, even at the group level. It should just scale all such betas uniformly.

I would expect any of GAM, SPMG1, BLOCK(0.6,1) or BLOCK(0.1,1) would be reasonable.

If you want to match very closely, SPMG1 might the basis function applied in SPM. There might also be differences in modeling drift. If you want to tell afni_proc.py to use sinusoids, that is an option, too.

- rick