Hi Dan,
Enorm is the Euclidean norm (sqrt(sum squares)) of the
backward difference of the motion parameters.
The backward difference at the first time point of each
run is always 0, and so then is the enorm.
To put it another way, at the beginning of a run, how
much motion was there between the current and previous
time point? Answer: we have no way to know.
For more details, see options -backward_diff, -collapse_cols
and -censor_motion in the output of
1d_tool.py -help.
- rick