Max motion displacement vs Motion limit

Hello AFNI gurus,

I am running the @ss_review_driver script and noticed that although our motion limit is set to 1mm, a few of our subjects had a max motion displacement of 1.29 for example, but then had 0 TRs excluded/censored for motion. Could someone clear up for me how this works? Thank you!!


When the motion parameters are evaluated for censoring, the first difference of the 6 parameters is applied, before taking the Euclidean norm (sqrt(sum squares)), giving the enorm file. So that is based on the different between adjacent time points.

The max motion displacement is a similar number, but it is between ANY pair of time points (before or after censoring). A very slow displacement drift will have low enorm values (first diff is always small), but the max difference could end up being large.

See also: -help_fields

Does that seem reasonable?

  • rick

Yes, thank you!