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

Clement Lee cll008 at eng.ucsd.edu
Thu Sep 5 09:11:15 PDT 2019


Nabil, does your pre-stimulus baseline overlap with post-stimulus data from
your previous trial? How much is this overlap?
Furthermore, from the averaged ERP I can clearly see 120 Hz noise. What
sort of preprocessing have you done? Did you use the suggested parameters
in Makoto's preprocessing pipeline
<https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline>?

Best,
Clement Lee
Applications Programmer
Swartz Center for Computational Neuroscience
Institute for Neural Computation, UC San Diego
858-822-7535


On Thu, Sep 5, 2019 at 2:43 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> 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
>>
>> _______________________________________________
>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
>> To unsubscribe, send an empty email to
>> eeglablist-unsubscribe at sccn.ucsd.edu
>> For digest mode, send an email with the subject "set digest mime" to
>> eeglablist-request at sccn.ucsd.edu
>>
>


More information about the eeglablist mailing list