[Eeglablist] ERSP : activity systematically shifted at t=0
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
Swartz Center for Computational Neuroscience
Institute for Neural Computation, UC San Diego
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:
> 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 :
> 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 ?
> *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
> Clement Lee
> Applications Programmer
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, UC San Diego
> 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) :
>> => 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 :
>> 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,
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