Could somebody please describe how the standardised version of DVARS is computed in fmriprep? (sorry if I missed this information)
I also noticed that, by default, fmriprep proposes a threshold of 1.5 std_DVARS to identify motion outliers / spikes. Do you have any additional suggestion on how to set this threshold value for spike detection?
The std_DVARS are essentially the non standard DVARS divided by the standard deviation of temporal difference time series. You can see the implementation of the DVARs algorithm in more depth here: