[Eeglablist] ERSP : activity systematically shifted at t=0

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Tue Sep 17 13:14:41 PDT 2019


Dear Alibou,

> But it's really strange considering that it's on all the frequencies

This means you have an impulse in the time domain.

> i create an algorithme for select the trials with strong and
strange activity at t = 0 for remove them.

t = 0? Looks like the noise is centered at t = -20 and t = 120. Anyway, you
must find the cause of the artifact in the single-trial time domain.

Makoto

On Fri, Sep 13, 2019 at 5:56 AM Alibou Nabil William Jean-Pierre <
nabil.alibou at epfl.ch> wrote:

> Dear makoto and Clement Lee,
> Thank you all for your help, the preprocessing i used is quite classic :
> 1. EOG/noisy channels removal
> 2. Epoch extraction corresponding to each events
> 3. Artifact removal with
> 4. Notch/comb notch filtering,
> 5. Low-pass filtering,
> 6. Interpolation of missing channels,
> 7. Epoching [-0.10 0.40] and baseline removal [-100 0].
> Then ICA (ICs, IC weights) were performed as well as the source
> localisation with Dipfit
>
> Right now i'm using the last solution i found : i create an algorithme for
> select the trials with strong and strange activity at t = 0 for remove
> them. I don't know about the origin of what appears to be an artifact (a
> device activated at t = 0 s ?). But it's really strange considering that
> it's on all the frequencies and that depending on the subjects, the
> activity may be positive, negative or both depending on the frequency.
>
>
> Best,
> ------------------------------
> *De :* eeglablist <eeglablist-bounces at sccn.ucsd.edu> de la part de Makoto
> Miyakoshi <mmiyakoshi at ucsd.edu>
> *Envoyé :* mercredi 11 septembre 2019 20:03:30
> *À :* eeglablist at sccn.ucsd.edu
> *Objet :* Re: [Eeglablist] ERSP : activity systematically shifted at t=0
>
> Dear Nabil,
>
> The figure you uploaded here https://imgur.com/dM28D4A strongly suggests
> the presence of impulse-like artifact before 0 ms and after 100 ms.
> This may be present only in one of the trials in high amplitude--so you
> want to check all the trials carefully.
>
> If you find the impulse is present at the fixed latency, then you have a
> good hope. You can use this tool to repair your data. This is the solution
> I wrote for simultaneous EEG-TMS to interpolate short-duration TMS artifact
> frames by using ARfit model.
> https://sccn.ucsd.edu/wiki/ARfitStudio
>
> You should provide us more systematic info for better solutions though.
> What was the task? What's the likely source of such impulse-like artifact?
> etc.
>
> Makoto
>
> On Thu, Sep 5, 2019 at 7:59 AM Alibou Nabil William Jean-Pierre <
> nabil.alibou at epfl.ch> wrote:
>
> > Hi Clement,
> > Thanks you for your response ! what is disturbing is that even with a
> > pre-stimulus baseline (i tested a lot of different baseline) and a erp
> > image which seems "normal" to me:
> > https://imgur.com/u7PHgW4
> >
> > I have an enormous activity (the values in the output ersp array are
> > extreme compared to other) at t = 0s and if i replace the data around 0
> by
> > the data before i will have this :
> >
> > https://imgur.com/dM28D4A
> > The peak of activity will surprisingly shift even more like this (i tried
> > to replace even a bigger part around t = 0s and still have this
> phenomenon).
> > Finally, i test to only plotted a part ([-200 100] ms) of my epoch
> > originally equal to [-250 500] ms and the activity won't be anymore
> around
> > t = 0s but 'graphically' at the same localisation !
> > => picture which shows this : https://imgur.com/q0y2HEb
> >
> > Is my eeglab haunted ?
> >
> >
> > Best,
> >
> > Nabil
> >
> >
> > ________________________________
> > De : Clement Lee <cll008 at eng.ucsd.edu>
> > Envoyé : mercredi 4 septembre 2019 23:34:19
> > À : Alibou Nabil William Jean-Pierre
> > Cc : eeglablist at sccn.ucsd.edu
> > Objet : Re: [Eeglablist] ERSP : activity systematically shifted at t=0
> >
> > Hi Nabil,
> >
> > There is always "activity" throughout an EEG recording (hopefully). I
> > don't use newtimef() regularly, but what shows up as red or blue blobs on
> > ERP/ERSP plots is dependent on how you epoch the data and how you choose
> > the baseline. It looks like your stimulus is 600 ms apart and the
> recording
> > is not that clean... and that you are using the full epoch as the
> baseline
> > for newtimef(). Before using time warping, have you checked out ERP
> image<
> > https://sccn.ucsd.edu/wiki/Chapter_08:_Plotting_ERP_images>?
> >
> > Best,
> > Clement Lee
> > Applications Programmer
> > Swartz Center for Computational Neuroscience
> > Institute for Neural Computation, UC San Diego
> > 858-822-7535
> >
> >
> > On Mon, Sep 2, 2019 at 4:21 AM Alibou Nabil William Jean-Pierre <
> > nabil.alibou at epfl.ch<mailto:nabil.alibou at epfl.ch>> wrote:
> > I am starting in the eeg analysis field and i was studying the TF
> analysis
> > of my dataset with newtimef()
> >
> > but i noticed that the activity, regardless of the event, was always at t
> > = 0s (and for every subject).
> >
> > Exemple of ERP/ERSP of components from my dataset (with extended epoch) :
> > https://imgur.com/ptEEpPD
> >
> > <https://i.imgur.com/ptEEpPD.png>https://imgur.com/yVgDg2k
> >
> > https://imgur.com/PLLqEMz
> > https://imgur.com/rUl0q8K
> > https://imgur.com/ftds9nY
> >
> >
> > => However if i test it with a constant signal with a spike at a certain
> > time the spectral activity displayed will be at the corresponding t.
> >  Im using this parameters :
> >
> > figure();
> >         newtimef(EEG.icaact(5,:,:), EEG.pnts, [EEG.xmin EEG.xmax]*1000,
> > EEG.srate,0,'freqscale','linear', ...
> >             'cycles',[5 0.5],'elocs', EEG.chanlocs, 'chaninfo',
> > EEG.chaninfo,  ...
> >             'freqs',[5 50], 'maxfreq',50,'baseline',[EEG.xmin
> > EEG.xmax]*1000,'trialbase', 'off','basenorm', 'off', 'plotitc', 'off',
> ...
> > % divise into 2 portions of frequencies for study easily ?
> >             'caption','test', 'padratio',
> > 4,'alpha',NaN,'ntimesout',100,'winsize',700, 'erspmax', 0.5);
> >
> > I have changed almost every parameter but i still have this problem and i
> > don't know the cause, thanks you in advance for your help.
> > Best regards,
> >
> > Nabil
> >
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>
> --
> Makoto Miyakoshi
> Assistant Project Scientist, Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
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-- 
Makoto Miyakoshi
Assistant Project Scientist, Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego


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