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

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Wed Sep 11 13:03:30 PDT 2019


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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