<div>Eduardo,</div><div> </div><div>Steve Luck's (2005) book <em>An Introduction to the Event-Related Potentials Method</em> has a chapter discussing reference methods. If you search the archives of the EEGLAB mailing list there are also many recent discussions (including references) about this issue.</div>
<div> </div><div>I am not personally experienced with spectral analyses, but in general, the online reference you use during the recording does not matter very much, since you can re-calculate the data to any other reference offline. For example, in both labs where I have done experiments, we use various online references but always re-reference to the average of both mastoids during the offline analysis; this is a common procedure, if you want to do that all you need to do is make sure to buy a cap that includes mastoid electrodes. Another common procedure is to use the average reference (see Luck (2005) or the EEGLAB online wiki for detailed discussion about average reference); for that, the most important thing is for the cap to have sufficient electrodes, evenly covering enough of the head. Of course, there are also many other referencing procedures available.</div>
<div> </div><div>Best,</div><div>Steve Politzer-Ahles<br><br></div><div class="gmail_quote"><blockquote style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid" class="gmail_quote">
<br>
<br>
<br>
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<br>
Message: 1<br>
Date: Mon, 25 Jun 2012 12:09:35 -0300<br>
From: Eduardo Schenberg <<a href="mailto:eduardoschenberg@gmail.com">eduardoschenberg@gmail.com</a>><br>
To: <a href="mailto:fieldtrip@science.ru.nl">fieldtrip@science.ru.nl</a><br>
Subject: [FieldTrip] EEG reference<br>
Message-ID: <<a href="mailto:7D53A322-3BF0-46F4-8D4B-B72E5B973EEC@gmail.com">7D53A322-3BF0-46F4-8D4B-B72E5B973EEC@gmail.com</a>><br>
Content-Type: text/plain; charset=us-ascii<br>
<br>
Hello all,<br>
<br>
I am new to this list, as I just started ding EEG experiments. I did some pilot tests with a BrainProducts/Brain Vision with an Acticap and I am doing some preliminary analysis using EEGLab/fieldtrip. I am now planning to buy my own EEG form Brain Products, but I am bothered by the fact that in most cap configs they sell, the reference is near Cz, usually FCz. As far as my knowledge goes, if I want to study power spectrum alterations and coherence in different frequencies between different electrodes, a reference in the head can be a problem, specially if some of the regions of interest are synchronous with the reference itself in the given frequency<br>
<br>
Can anyone point me to some good review or chapter about these issues so I can study them better and buy the best config available?<br>
<br>
Many many thanks for all<br>
<br>
eduardo schenberg<br>
<br>
<br>
<br>
<br>
<br>
------------------------------<br>
<br>
Message: 2<br>
Date: Tue, 26 Jun 2012 11:31:32 +0200<br>
From: Marcel Heers <<a href="mailto:marcel.heers@googlemail.com">marcel.heers@googlemail.com</a>><br>
To: <a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a><br>
Subject: [FieldTrip] Source localization using DICS for EEG data from<br>
combined MEG/EEG recordings<br>
Message-ID:<br>
<CAMq9WnPig4WAhsiM5ogwnXrPcPWj34TyWv8JuTAus5f=<a href="mailto:xNecrA@mail.gmail.com">xNecrA@mail.gmail.com</a>><br>
Content-Type: text/plain; charset=ISO-8859-1<br>
<br>
Dear all,<br>
<br>
I am trying to perform source localization in the frequency domain<br>
from EEG data using DICS. The data were recorded combined with MEG<br>
(Neuromag data format). The volume conductor is a 3 shell realistic<br>
head model created with bemcp.<br>
When running DICS with the following settings<br>
<br>
cfg = [];<br>
cfg.method = 'dics';<br>
cfg.grad = elec;<br>
cfg.frequency = 14;<br>
cfg.vol = vol_eeg;<br>
cfg.dics.projectnoise = 'yes';<br>
cfg.dics.lambda = 5;<br>
source = ft_sourceanalysis(cfg, freq);<br>
<br>
<br>
I am am getting the following error message:<br>
<br>
??? Error using ==> svd<br>
Input to SVD must not contain NaN or Inf.<br>
<br>
Error in ==> beamformer_dics>pinv at 568<br>
[U,S,V] = svd(A,0);<br>
<br>
Error in ==> beamformer_dics at 314<br>
filt = pinv(lf' * invCf * lf) * lf' * invCf; %<br>
Gross eqn. 3, use<br>
PINV/SVD to cover rank deficient leadfield<br>
<br>
Error in ==> ft_sourceanalysis at 584<br>
dip(i) = beamformer_dics(grid, sens, vol, [],<br>
squeeze(Cf(i,:,:)), optarg{:});<br>
<br>
<br>
and I am not sure what might be the cause.<br>
<br>
Maybe anyone can help me! Thank you in advance!<br>
<br>
Marcel<br>
<br>
<br>
------------------------------<br>
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End of fieldtrip Digest, Vol 19, Issue 42<br>
*****************************************<br>
</blockquote></div><br><br clear="all"><br>-- <br>Stephen Politzer-Ahles<br>University of Kansas<br>Linguistics Department<br><a href="http://www.linguistics.ku.edu/">http://www.linguistics.ku.edu/</a><br>