update: artifact detection

georges Otte georges.otte at PANDORA.BE
Fri Feb 3 09:41:01 CET 2006


Hi,

I saw some paper from a group in Leuven eliminating EMG artefact based
on the canonical component analysis (another Blind Source method).
Google it with CCA- EEG. It worked very fast. I think that ANT compagny
is looking into porting this into their standard software. The method is
based on the difference in aotocorellation between EEG and EMG signals.

Hope this helps,


Georges
------------------------------------
Neurologpsychiatrie EEG-EMG
Otte Georges
Dr.
georges.otte at pandora.be
Bijlokehof 24
9000 Gent
tel: 09 329 06 62
fax: 09 282 26 72
mobile: 0478 205 202
------------------------------------


> -----Original Message-----
> From: FieldTrip discussion list
> [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf Of Dr. Jose Luis
> Patino Vilchis
> Sent: vrijdag 3 februari 2006 8:45
> To: FIELDTRIP at NIC.SURFNET.NL
> Subject: Re: [FIELDTRIP] update: artifact detection
>
>
> Dear Robert,
>
> Is it there a paper explaining how the muscle artifact
> rejection is done?
>
> best regards
>
> Luis Patino
>
>
> Zitat von Marcel Bastiaansen <Marcel.Bastiaansen at fcdonders.ru.nl>:
>
> > Dear Robert,
> >
> > Thanks for updating the functions. They generally look much better
> > now. I have a slight problem however. For certain types of analysis
> > (e.g.
> > multitaper) I need some data before and after the actual
> trials in my
> > experiment (to allow tapers to shift into the data at the
> beginning of
> > the trial, and out of the data at the end of the trial).
> Usually I cut
> > my data so that these extra datapoints are part of the
> 'trial', but I
> > don't check these extra datastretches for EOG artefacts (as
> they fall in
> > the ITI they typically contain a lot of blinks). I used to
> do that  by
> > specifying a negative padding value in the artefact_eog
> function, but
> > that is no longer possible. Hence, my question is, whether
> it would be
> > possible to include the option of checking only a
> user-specified part of
> > each trial for artefacts.
> > Another thing is that it is not (yet?) possible to call the
> old artefact
> > routines in the way you specified it in your message below
> (though it is
> > possible to directly call the artefact_eog_old function).
> >
> > Best,
> > Marcel
> >
> >
> > Robert Oostenveld wrote:
> >
> > > Dear Fieldtrip users,
> > >
> > > I have updated the artifact detection functions
> (artiact_xxx, where
> > > xxx=jump, eog and muscle). Each of these three functions
> was already
> > > based on the same underlying idea, namely to filter and
> preprocess
> > > the data, then z-transform the result, cummulate the
> z-values over
> > > channels and finally look for z-values that are larger than the
> > > cutoff level. To reflect this similarity, I have created a new
> > > function: artifact_zvalue. Each of the artifact_jump, eog
> and muscle
> > > functions now sets some default values and then calls
> > > artifact_zvalue. That facilitates the maintenance and
> ensures that
> > > all functions behave the same regarding graphical
> feedback. From now
> > > on, you can also visually verify the trial definition and the
> > > detected artifacts in rejectartifact, using
> cfg.artfctdef.feedback=yes.
> > >
> > > Most important for you to know is that:
> > > 1) the new functions should be largely backward compatible. The
> > > filtering and preprocessing computations were only marginally
> > > changed, so the outcome should be almost the same.
> > > 2) the padding has been better defined. I will also write
> an artifact
> > > detection tutorial that explains these padding values better.
> > > 3) the new artifact detections functions (for jump, eog
> and muscle)
> > > now only will work on continuous and pseudo-continuous
> data. Jumps in
> > > the data at the trial boundaries for non-continous data
> are not dealt
> > > with and will mess up the result so --if you want to use them on
> > > trial-based data-- you are responsible yourself for
> configuring the
> > > padding options correctly.
> > > 4) the old functions are still available, with the name
> > > artifact_xxx_old (where xxx=jump, eog and muscle). If you
> want to use
> > > them, you should specify cfg.artifact.type={'eog_old',
> ...} and call
> > > the rejectartifact function.
> > >
> > > The idea (which I will describe in the upcoming "artifact
> tutorial")
> > > is that you do not use cfg.rejectjump/muscle/eog=yes any
> more in the
> > > preprocessing cfg structure, but that you do the following steps
> > > seperately:
> > >   cfg = something to start with...
> > >   cfg = definetrial(cfg)
> > >   cfg = artifact_eog(cfg)
> > >   cfg = artifact_eog(cfg)
> > >   cfg = artifact_jump(cfg)
> > >   cfg = artifact_muscle(cfg)
> > >   cfg = rejectartifact(cfg)
> > >   data = preprocessing(cfg)
> > >
> > > The fieldtrip version on home/common (inside the FCDC) will be
> > > updated this afternoon. The fieldtrip version on the ftp server
> > > (outside the FCDC) will be updated this evening.
> > >
> > > Since it is a large change in the fieldtrip code, bugs might have
> > > crept in. Please be extra cautious the upcoming time and report
> > > unusual behaviour. Sorry for the inconvenience that this
> may result in.
> > >
> > > best regards,
> > > Robert
> > >
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > Robert Oostenveld, PhD
> > > F.C. Donders Centre for Cognitive Neuroimaging
> > > Radboud University Nijmegen
> > > phone: +31-24-3619695
> > > http://www.ru.nl/fcdonders/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >
> >
> > --
> > dr. Marcel C.M. Bastiaansen.
> > FC Donders Centre for Cognitive Neuroimaging
> > Visiting address: Kapittelweg 29, 6525 EN Nijmegen, the Netherlands
> > Mailing address: Trigon 181, PO Box 9101, 6500 HB Nijmegen,
> the Netherlands
> > phone: + 31 24 3610 882
> > fax:   + 31 24 3610 989
> > mail: marcel.bastiaansen at fcdonders.ru.nl
> > web:
> >
> http://www.ru.nl/aspx/get.aspx?xdl=/views/run/xdl/page&ItmIdt=
> 20592&SitIdt=119&VarIdt=96
> > --
> >
> >
>
>



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