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<p class=MsoNormal><font size=2 color=navy face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;color:navy'>In the “ancient
times”, I used a Faraday cage to eliminate external electromagnetic
noise, today EEG recording systems use filters and can <st1:PersonName
ProductID="be used in a" w:st="on">be used in a</st1:PersonName> hospital
environment, but I see the same problems in a lot of circumstances. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;color:navy'>Maybe using special
wallpapers creating a Faraday cage should be used more frequently?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span lang=EN-GB
style='font-size:10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><st1:PersonName ProductID="Patrick De Wit" w:st="on"><b><i><font
size=3 color=green face="Times New Roman"><span lang=NL-BE style='font-size:
12.0pt;color:green;font-weight:bold;font-style:italic'>Patrick De Wit</span></font></i></b></st1:PersonName><font
color=navy><span style='color:navy'> <br>
</span></font><font size=2 color=navy><span lang=NL-BE style='font-size:10.0pt;
color:navy'>Neurologist</span></font><font color=navy><span style='color:navy'><br>
<a href="mailto:p.de.wit@telenet.be"
title="blocked::mailto:p.de.wit@telenet.be
mailto:p.de.wit@telenet.be"><font
size=2 color="#df0a00"
title="blocked::mailto:p.de.wit@telenet.be
mailto:p.de.wit@telenet.be"><span
title="blocked::mailto:p.de.wit@telenet.be
mailto:p.de.wit@telenet.be"><span
title="blocked::mailto:p.de.wit@telenet.be
mailto:p.de.wit@telenet.be"><span
lang=NL-BE style='font-size:10.0pt;color:#DF0A00'><span
title="blocked::mailto:p.de.wit@telenet.be"><span
title="blocked::mailto:p.de.wit@telenet.be">p.de.wit@telenet.be</span></span></span></font></span></span></a>
</span></font><o:p></o:p></p>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>Van:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:windowtext'> Andre Achim [mailto:achim.andre@uqam.ca] <br>
<b><span style='font-weight:bold'>Verzonden:</span></b> donderdag 10 januari
2008 21:21<br>
<b><span style='font-weight:bold'>Aan:</span></b> 'Tim Mullen'<br>
<b><span style='font-weight:bold'>CC:</span></b> eeglablist@sccn.ucsd.edu<br>
<b><span style='font-weight:bold'>Onderwerp:</span></b> [Eeglablist] RE : line
noise removal issues</span></font><font color=black><span style='color:windowtext'><o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>I once observed that fluorescent lighting
tends to inject odd harmonics of the line noise in the EEG. Fluorescent tubes
even in an adjacent room could well be responsible for these artefacts. I think
that dimmers on incandescent lights are also susceptible to produce artefacts.
Lights functioning on DC are safer in an EEG lab.</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<div>
<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>I am sending this in case it may help.</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=2 color=blue face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:blue'>André Achim</span></font><o:p></o:p></p>
</div>
<blockquote style='margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt'>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=2 color=black
face=Tahoma><span lang=FR style='font-size:10.0pt;font-family:Tahoma'>-----Message
d'origine-----<br>
<b><span style='font-weight:bold'>De :</span></b>
eeglablist-bounces@sccn.ucsd.edu [mailto:eeglablist-bounces@sccn.ucsd.edu] <b><span
style='font-weight:bold'>De la part <st1:PersonName ProductID="de David" w:st="on">de<span
style='font-weight:normal'> David</span></st1:PersonName><span
style='font-weight:normal'> Contreras Ros<br>
</span>Envoyé :</span></b> 10 janvier 2008 09:54<br>
<b><span style='font-weight:bold'>À :</span></b> Tim Mullen<br>
<b><span style='font-weight:bold'>Cc :</span></b> eeglablist@sccn.ucsd.edu<br>
<b><span style='font-weight:bold'>Objet :</span></b> Re: [Eeglablist] line
noise removal issues</span></font><span lang=FR><o:p></o:p></span></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Try SOBI instead of ICA infomax. It seems to isolate
line noise better (at least from my limited experience). SOBI is also
implemented in EEGLAB.<br>
<br>
Regards, <br>
<br>
David.<br>
<br>
Tim Mullen wrote: <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Dear EEGLAB users,<br>
<br>
I have a question regarding the use of ICA for line noise removal.<br>
<br>
I have some electrocorticographic (ECoG) data with a strong 60Hz line noise
artifact as well as a 180Hz harmonic (only odd harmonics seem to be present,
probably due to symmetrical clipping). <br>
<br>
I am applying frequency-domain granger causality to this data, but have run
into some serious problems with the presence of this line noise. Oddly enough,
the line noise dominates as a <i><span style='font-style:italic'>directional </span></i>effect
in the granger causality (unless there is an apparent temporal delay between
channels at 60 Hz, a peak at 60 Hz should only be present in the instantaneous
causality). This is likely because the phase at 60Hz appears to differ between
channels. The strength of the directional effect at 60 and 180Hz is so strong
that it dominates any other interesting nearby features, making it impossible
to analyze causal interactions within a wide range of frequencies of interest. <br>
<br>
The noise band is far too wide for notch filtering to be considered a suitable
solution. I have then tried extended infomax ICA (as implemented in
EEGLAB's <i><span style='font-style:italic'>runica</span></i> function), to
isolate the subgaussian noise components. I have attempted this both in
automatically estimating the number of sub-gaussian sources and also fixing the
number of subgaussian sources to 1, 2, etc. None of these approaches have been
successful. ICA appears to converge properly and the covariance matrix of
the estimated components is the identity matrix (it's at least second-order independent).
<br>
<br>
It is possible that the tanh function used to model the subgaussian source
distributions is unsuitable for this line noise source. Has anyone used or
implemented any other families of distributions to calculate the score function
for ICA?<br>
<br>
Des anyone have any recommendations on how to remove this line noise, either
via source separation or other techniques? In particular, if anyone has
developed a plugin for EEGLAB or their own code for automatic line noise
removal, that would be optimal. <br>
<br clear=all>
<br>
Thanks much for your input!<br>
<br>
Regards,<br>
Tim <o:p></o:p></span></font></p>
<pre style='text-align:center'><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt'>
<hr size=4 width="90%" align=center>
</span></font></pre><pre><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt'><o:p> </o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>_______________________________________________<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>eeglablist mailing list <a
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