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

Clement Lee cll008 at eng.ucsd.edu
Wed Sep 4 16:34:19 PDT 2019


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
>
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