Hi AFNI experts,
When using “-censor_motion” in an “1d_tool.py” command, “enorm.1D” was acquired. In the “enorm.1D” file, I wonder why the first TR has the numerical value 0.
And when we set the numerical value behind “-censor_motion” and got “censor.1D” file, I wonder if “censor.1D” is based on “enorm.1D” or not. Because I set “-censor_motion 0.2” and found that in the specific TR, it has the value less than 0.2 in “enorm.1D”, but it got 0 in “censor.1D”, which made me a little confused.
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.
Thank you, Rick
I got a rough understanding of “enorm”
I also wonder if the use of option"demean" and when to use it?
The motion parameters are de-meaned in a typical
proc script for use as regressors of no interest.
However that makes basically no difference, except
to affect the constant polort terms. It also makes no
difference in computing the backward difference used
for the enorm.
It is a convenience option for those that want to use it.