[Eeglablist] Lowpass filtering after preprocessing

Andreas Widmann widmann at uni-leipzig.de
Sat Mar 4 04:58:13 PST 2017


> I have another filter related question that I hope you can help me with. 
> 
> I'm currently preprocessing subjects from different locations and I've been able to use cleanline to remove line noise in about half the EEGs. However, for the other half cleanline doesn't seem to work (too much spanning from 57-63 Hz) and I have applied a notch filter for those. Is there any methodological problem with this approach (half the participants cleanline and half notch filter) when comparing groups? Of cause, there is an equal amount of pre and post for the two groups.
This depends on your further analysis. Personally, I try to keep pre-processing identical for all subjects but this is only a personal preference and not a recommendation based on empirical support. I suggest to directly compare the data and results of your approach and data and results pre-processed with notch for all subjects.

Best,
Andreas

>  
> 
> Thanks a lot,
> 
> Eric
> 
> 
> On Thu, Mar 2, 2017 at 11:35 PM, Eric HG <erichg2013 at gmail.com> wrote:
> Thanks a lot Andreas for your reply!
> 
> Best,
> 
> Eric
> 
> On Wed, Mar 1, 2017 at 2:31 PM, Andreas Widmann <widmann at uni-leipzig.de> wrote:
> PS: Resampling -> filtering should be considerably faster than filtering -> resampling.
> 
> > Am 01.03.2017 um 14:09 schrieb Andreas Widmann <widmann at UNI-LEIPZIG.DE>:
> >
> > Hi Eric,
> >
> >> I have an additional question: Does it matter when you perform resampling? Can it be done both before and after filtering? I've been doing it after filtering and it seems to work well.
> > These are all linear operations, so it actually shouldn’t matter (if done before epoching as also resampling implies filtering; IIRC there were also other problems with resampling of epoched data but I do not remember the details).
> >
> > Best,
> > Andreas
> >
> >> Best,
> >>
> >> Eric
> >>
> >> On Tue, Feb 28, 2017 at 2:52 PM, Andreas Widmann <widmann at uni-leipzig.de> wrote:
> >> Hi Eric,
> >>
> >>> Would it be better if I remove the epochs and go "back" to continous data and then filter and epoch again? Or doesn't that make any difference?
> >> Not sure what you mean by ""back" to continous data“. You mean just concatenating the epochs? This would make things worse. Or filtering the original really continuous data? This should make the difference.
> >>
> >> Would it be ok to keep the discussion on list? Best,
> >> Andreas
> >>
> >>>
> >>> Best,
> >>>
> >>> Eric
> >>>
> >>> On Tue, Feb 28, 2017 at 11:14 AM, Andreas Widmann <widmann at uni-leipzig.de> wrote:
> >>> Hi Eric,
> >>>
> >>> I recommend not to filter epoched data unless absolutely necessary. Any filter implementation has to extrapolate the signal at the (epoch) edges the one or the other way possibly introducing edge effects depending on the signal and extrapolation algorithm (possibly also affecting phase). Edge effects are indeed usually less pronounced and problematic for lowpass filters than for highpass filters but cannot be excluded in general.
> >>>
> >>> Hope this helps! Best,
> >>> Andreas
> >>>
> >>>> Am 27.02.2017 um 18:18 schrieb Eric HG <erichg2013 at gmail.com>:
> >>>>
> >>>> Hi everyone,
> >>>>
> >>>> Is there any problem to perform lowpass filtering after preprocessing when preprocessing includes the following:
> >>>> High- and low-pass filtering, cleanline, epoching, removal of epochs, average referencing and ICA?
> >>>>
> >>>> Thanks a lot,
> >>>>
> >>>> Eric
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> >>>
> >>
> >>
> >
> 
> 
> 
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