Hi Alfonso,
Thank you very much for your immediate reply. I have another questions: firstly, I found the default rotation threshold  is 0.02, but I am not sure what is the unit of this threshold, degree?. Secondly, the motion is closely related to task in my experiment. So, the  signal-task correlation is more than 0.2 (see attached example). But, I don't know whether it is a high rate. Could you share me some experience about that.
Thanks a lot in advance！
Ivan