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<div class="moz-cite-prefix">I would just like to note that in the
examples I have seen, these components are not limited to "line
noise" components. <br>
<br>
Luca<br>
<br>
On 04/06/2017 11:49 AM, Jason Palmer wrote:<br>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Hi
Julia,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">I
think Luca is probably right, the “flat” components are
usually line noise (common mode). You can verify that by
looking at the component activation (using plot component
activations) corresponding to that map. It should be
sinusoidal, with 50 or 60 cycles per second. Also the
associated spectrum should have a huge peak at 50 or 60 Hz.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">The
appearance of line noise maps depends on the recording
environment, and the referencing. Average referencing will
usually leave some line noise, and then if ICA separates out
the residual line noise, the map be compact rather than
flat. In my experience, I often see line noise maps that
look like frontal midline (brain component) maps, but are
actually residual line noise.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Looking
at the component activation is usually a pretty good way to
determine whether a component is a “good” brain component,
or “noise” or artifact.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Jason<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
<a class="moz-txt-link-abbreviated" href="mailto:eeglablist-bounces@sccn.ucsd.edu">eeglablist-bounces@sccn.ucsd.edu</a>
[<a class="moz-txt-link-freetext" href="mailto:eeglablist-bounces@sccn.ucsd.edu">mailto:eeglablist-bounces@sccn.ucsd.edu</a>] <b>On Behalf
Of </b>Luca Pion-Tonachini<br>
<b>Sent:</b> Thursday, April 06, 2017 7:20 AM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:eeglablist@sccn.ucsd.edu">eeglablist@sccn.ucsd.edu</a><br>
<b>Subject:</b> Re: [Eeglablist] All red or blue ICA<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">Hi Julia,<br>
<br>
I've seen the before as well and my personal theory is that
they are due to common mode noise (though I don't have
direct proof). If you change your data to using a common
average reference, I think they should go away. That would
also explain why your data looks cleaner without them, as
you are essentially removing the common mode noise (albeit
in an roundabout way).<br>
<br>
Luca<br>
<br>
On 04/05/2017 08:24 AM, Julia Basso wrote:<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal"><span style="font-size:9.5pt">Dear all,</span>
<o:p></o:p></p>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt">I have
a 20 channel EEG system and after cleaning the data by
first conducting a band pass filter than cleaning
epoched data by visual inspection, I am running ICA to
detect and remove eye blinks and eye movements. <o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt">My
question is in regards to ICs that are distinctly all
blue or all red. My instinct is to remove these ICs
(and when I do, the data looks cleaner)- but I wanted
to get your opinion. What does this type of IC
indicate? Is it merely noise in the system?<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt">Best,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:9.5pt">Julia<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p class="MsoNormal">-- <o:p></o:p></p>
<div>
<div>
<div>
<div>
<div>
<div>
<p class="MsoNormal"><i>Julia C. Basso, PhD, CYT</i>
<o:p></o:p></p>
<div>
<p class="MsoNormal"><i>Post-doctoral Research
Associate</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"><i>New York University</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><i>Center for Neural
Science</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><i>Suzuki Laboratory</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><i>4 Washington Place,
Room 809</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><i>New York, NY 10003</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><i>(212) 998-3969</i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:9.5pt"><a
moz-do-not-send="true"
href="http://www.juliabasso.com"
target="_blank">www.juliabasso.com</a></span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><i><span
style="font-size:9.5pt"><a
moz-do-not-send="true"
href="http://www.suzukilab.com"
target="_blank">www.suzukilab.com</a></span></i><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</div>
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</div>
<p class="MsoNormal"><br>
<br>
<br>
<o:p></o:p></p>
<pre>_______________________________________________<o:p></o:p></pre>
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