[Eeglablist] epoch extracting

Tue Jun 25 20:22:56 PDT 2013

Dear Tahini,

I agree with Stephen and Carlos. Why don't you use an epoch long enough to
covers the longest trial.

EEGLAB does not take variable epoch lengths because you can't create a
matrix with different length of data with Matlab (unless you pad them with
NaN, but this will introduce problems in computation).

Makoto

2013/6/25 Carlos Andrés Guerrero M. <cguerrero76 at yahoo.com>

> Dear Tahani,
> You need a tigger signal for that. At the end the problem consist just in
> finding the correct value in the tigger (correspond to press button) signal.
> Best regards,
> Carlos
>
>   ------------------------------
>  *De:* T. Almabruk <t.almabruk at yahoo.com>
> *Para:* "mmiyakoshi at ucsd.edu" <mmiyakoshi at ucsd.edu>; "
> eeglablist at sccn.ucsd.edu" <eeglablist at sccn.ucsd.edu>
> *Enviado:* Lunes, 24 de junio, 2013 7:33 A.M.
> *Asunto:* [Eeglablist] epoch extracting
>
> Dear Makoto
>
> I want to know if there is a possibilities to extract epochs with
> inconstant lengths.
> I have a continues EEG dataset where the participant can spend as long
> time as he/she wants before responding (press the button) to the presented
> stimuli. So based on that, this dataset contains  stimuli with very quick
> responses and others with very late responses(in some cases more than 2.5
> min).
> Can you please suggest me how to deal with this case
>
> Cheers,
> Tahani
>
>    *From:* Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> *To:* T. Almabruk <t.almabruk at yahoo.com>; EEGLAB List <
> eeglablist at sccn.ucsd.edu>
> *Sent:* Friday, May 31, 2013 3:01 AM
> *Subject:* Re: [Eeglablist] EEG Coherence combination
>
> Dear Tahani,
>
> Check out SIFT by Tim Mullen
> http://sccn.ucsd.edu/wiki/SIFT
>
> When you compute coherence measures, it generates EEG.Conn.... you can
> simply average them across all channels. FYI, averaging across column gives
> you information outflow, and across raw gives you information inflow.
>
> Makoto
>
>
> 2013/5/29 T. Almabruk <t.almabruk at yahoo.com>
>
> Hi List
> I have a question about combining coherence measurement for multi
> electrodes. I mean If I calculate the coherence between each pair in a
> dataset of 40 electrodes. Is there any way to combine theses measurements
> in one measure I need a way better that averaging. or any idea that help me
> to have just one measurement instead of this big number of measurements
>
> Cheers,
> Tahani
>
>    *From:* Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> *To:* T. Almabruk <t.almabruk at yahoo.com>
> *Sent:* Thursday, April 25, 2013 3:40 AM
> *Subject:* Re: [Eeglablist] EEG Coherence
>
> Dear Tahani,
>
> Ok I see. Most likely, the difference between the two results are due to
> the difference of parameters you used. Unfortunately I'm not familiar nor
> interested in pop_newcrossf() especially at the scalp channel level-because
> we have SIFT- I won't compare the details in these two methods.
>
> So I have no answer to your question technically, but starategically I can
> recommend that you use SIFT instead. It addresses many theoretical problems
> you run into when performing coherency analysis. Google SIFT Tim Mullen. He
> is one of our genius guys.
>
> Makoto
>
>
> 2013/4/19 T. Almabruk <t.almabruk at yahoo.com>
>
> Dear  Makoto
>
> Thanks alot for your reply. I will try to explain my problem so that may
> give you an idea about what i am trying to do. Simply i try to make a
> comparsion between calculating cross-coherence between two channals using
> first pop-newcrossf() and second by Mscoher.
> I followed the next steps:
> 1- I filtered the signals
> 2- extract the epoches
> 3-run ICA
> 4- i used pop_newcrossf() to calculate the cross-coherence between channel
> CP1(17) and CP2(18) in the first case as can be seen in the attached
> figures.
>
> http://www.flickr.com/photos/94417587@N05/
>
>  and then repeated the same steps with channel T7(11) and channel T8 (15).
>
> on the othere hand,
>  i calculated the cross-coherence between the same channals by using
> MSCOHER matlab function, i used the data after extracting epoches but
> without runing ICA.
>
> fs=128;
> % sampling frequency
> nfft=256;
> % width of subseries (# of samples)
>  ww=256;
> % width of hanning window applied to each subseries
> over=0;
> s_1=EEG.data(11,:);
> s_2=EEG.data(15,:);
>  q=mscohere(s_1,s_2,hanning(ww),over,nfft,fs);
>  figure
>  plot(q(1:50),
> 'b');
> ylabel(
> 'Coherence');
> xlabel(
> 'Frequences');
>
> *I can see a difference between the results in both cases i mean the
> coherence between the channals by using newcross() and that by using
> Mscoher!!!!*
> **
> *I am sure that i still missunderstand something*
> *and i'm willing to get help from you*
> **
> *Cheers,*
> *Tahani*
>
>   *From:* Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> *To:* T. Almabruk <t.almabruk at yahoo.com>
> *Cc:* "eeglablist at sccn.ucsd.edu" <eeglablist at sccn.ucsd.edu>
> *Sent:* Tuesday, April 2, 2013 8:36 AM
> *Subject:* Re: [Eeglablist] EEG Coherence
>
>  Dear Tahani,
>
> Looks like your channel 1 and 2 are very much alike. Did you choose two
> ICs? Did you choose subspace of alpha or mu that are similar to each other?
>
> If there were coherence of near 1 between two ICs that do not belong to
> the same subspace (and I guess that's the case here), something should be
> wrong because they are far from independent. Why don't you check the setup
> and tell us more detail about the comparison?
>
> Makoto
>
>
>
>
> 2013/3/27 T. Almabruk <t.almabruk at yahoo.com>
>
>
>
>    Hi List
>
> I asked a question before about measuring EEG coherence by EEGLAB. I got
> benifits from the answer i got  but still have something wrong. I applied
> the function to the same dataset provided with EEGLAB tutorial. i filtered
> the data first and then extract the epoches (153). After that i run ICA and
> ploted component cross-coherence between channel 4 and channel 9.
> As you can see fig(1) was the result and i tried to zoom it in (fig 2).
> I wanted to compare the result with that can be done by matlab function
> (Mcoher) and fig(3) represents the results i got.
> My question is that, there is a big difference in the coherence's
> amplitude between the two functions where using EEGLAB the amplitude is
> less that 0.1 where with Mcohere as you can see is close to 1.
>
> I'm sure i miss undeerstand something because i'm new with this area and
> hope i can find some help from you .
>
> Cheers,
> Tahani
>
>
> http://www.flickr.com/photos/94417587@N05/
>
>
>
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>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
>
>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
>
>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
>
>
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>

-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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