Hello, I recently learned about the ART toolbox and I have a few questions that I couldn't get answers to from the manual:

1. Is there a way to analyze between-group differences in stimulus-correlated motion?
2. Power spectra- How does one find the high pass cut-off frequency value? And again, is there a way to do it at a group level?
3. Motion-task correlation-what is the correlation value above which we should worry about the motion-task correlation? I heard it was about 0.2 but I don't know why? 
4. At an individual level, if I were to find that few subjects show significant stimulus correlated motion for specific conditions, how does one counter this problem? Include the SPM regressor file as 1st-level covariate during the analysis?