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<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=265451520-10012008>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></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=265451520-10012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=265451520-10012008>I am
sending this in case it may help.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=265451520-10012008></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=265451520-10012008>André
Achim</SPAN></FONT></DIV>
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<DIV></DIV>
<DIV class=OutlookMessageHeader lang=fr dir=ltr align=left><FONT face=Tahoma
size=2>-----Message d'origine-----<BR><B>De :</B>
eeglablist-bounces@sccn.ucsd.edu [mailto:eeglablist-bounces@sccn.ucsd.edu]
<B>De la part de</B> David Contreras Ros<BR><B>Envoyé :</B> 10 janvier
2008 09:54<BR><B>À :</B> Tim Mullen<BR><B>Cc :</B>
eeglablist@sccn.ucsd.edu<BR><B>Objet :</B> Re: [Eeglablist] line noise
removal issues<BR><BR></FONT></DIV>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:
<BLOCKQUOTE
cite=mid:1e7cfd2c0712101556l6c7f3cb3ycb46746458609b2c@mail.gmail.com
type="cite">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>directional </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>runica</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><SPAN
style="FONT-SIZE: 16px; FONT-FAMILY: Times"></SPAN><BR clear=all><BR>Thanks
much for your input!<BR><BR>Regards,<BR>Tim <PRE wrap=""><HR width="90%" SIZE=4>
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