[Mne_analysis] Signal processing

[Matti Hamalainen]

On Jan 21, 2010, at 3:25 PM, Ghuman, Avniel (NIH/NIMH) [F] wrote:

> Hi Linda,
>
> In fact, you almost certainly want to first do artifact rejection  
> then filter, then the last two the order makes no difference.  The  
> reason being that filters take time to settle.  If you average  
> first, you will have large filter artifacts at the beginning and  
> ends of each trial (you would much rather put these artifacts on the  
> beginning and ends of each run and then just leave extra time in the  
> beginning and ends of runs that you do not analyze).  There are  
> filter tricks that can be done to minimize these edge effects, but  
> in my experience the mne stream does leave substantial filter  
> artifacts at the beginning and ends of runs.  You would have to  
> write your own filter (which you may have already done) if you want  
> to avoid these.

Hi Linda,

Just to clarify: if there is a significant dc offset in the data,  
there is, indeed, ringing in the mne_browse_raw/mne_process_raw  
filters in the beginning and possibly at the end of the runs but *not*  
for each trial. Usually this is no big concern.

MNE filters first and then check for artifacts. The reasoning for this  
is that the purpose of a filter is to reject noise which you do not  
want to mistake for an artifact because it will be removed by the  
filter anyways.

- Matti




---------

Matti Hamalainen, Ph.D.
Athinoula A. Martinos Center for Biomedical Imaging
Massachusetts General Hospital

msh at nmr.mgh.harvard.edu






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