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Dear Maarten,<br>
<blockquote type="cite"
cite="mid1113920755.426514f363d58@webmail1.kuleuven.be">
<pre wrap="">after successfully running ICA on epoched data to remove eyemovement
artifacts, I want to run ICA again on the filtered epochs to remove
other artifact components. I do not want to work with the remaining
components of the first ICA as these epochs can differ a lot from the
task related epochs I want to use.
</pre>
</blockquote>
Since you seem to have different data epochs (between the first ICA
pass on all your data, and the second one on your task related epochs),
it is OK to rerun ICA (it is useless to rerun ICA on the same data
epochs; see the tutorial for more details). In theory, it should not be
necessary to change any parameter since you do not use exactly the same
data epochs. However, since the algorithm does not seem to converge
with your data, you probably have a large amount of common data epoch,
so you should use the 'pca' option to reduce the number of dimensions.
If you removed 10 artifactual components and have 64 electrodes, use
the option " 'pca', 54 ".<br>
<br>
Note that you choose to run ICA on your task related epochs only. We
usually use all the data available to perform ICA decomposition and
then study components that vary between experimental conditions. The
reason for using as much data as possible is that we realized that ICA
(at least Infomax ICA, the default option) returns "nicer" components
(i.e. component which can be modeled using a single equivalent dipole)
as the amount of data increases. The reason why ICA finds more
cognitively related components as you increase the amount of data is
that cognitive components tend to be expressed over the whole data. In
contrast, electrical artifacts are usually only expressed transiently,
so, as you increase the amount of data, the relative proportion between
cognitive and electrical artifacts is increasing. As a consequence, the
number of component ICA will dedicate to the cognitive components will
also increase. This is our hypothesis at least.<br>
<br>
Hope this help,<br>
<br>
Arno<br>
<blockquote type="cite"
cite="mid1113920755.426514f363d58@webmail1.kuleuven.be">
<pre wrap="">However, for some unclear reason the ICA procedure starts stalling at
the "Beginning ICA training..." print. Sometimes it gets to lowering its
learning rate and starting again, but I tend to abort the thing after
half an hour.
Running the ICA for removing the eyemovements was no problem at all. It
never took more than one ore two minutes. Even when I used it on more
epochs than what I'm trying to now.
What could be the problem?
thanks,
maarten
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</pre>
</blockquote>
<br>
<br>
<div class="moz-signature">-- <br>
<br>
<b><font face="Arial,Helvetica"><font size="+1">Arnaud Delorme, Ph.D.</font></font></b>
<br>
<font face="Arial,Helvetica"><font size="+1"><font color="#3333ff">Swartz
Center for Computational Neuroscience,</font> <font color="#3333ff">INC,
University of San Diego California</font></font></font>
<br>
La Jolla, CA92093-0961, USA
<p><font face="Arial,Helvetica"><b>Tel</b> :<i>(+1)-858-458-1927 ext 15</i></font>
<br>
<font face="Arial,Helvetica"><b>Fax</b> :<i>(+1)-858-458-1847</i></font>
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<font face="Arial,Helvetica"><b>Web page</b>: <a
href="http://www.sccn.ucsd.edu/%7Earno">sccn.ucsd.edu/~arno</a></font>
<br>
<font face="Arial,Helvetica"><b>To think upon</b>:</font></p>
<blockquote><dt><font face="Arial,Helvetica"> The ultimate measure of a
man is not where he stands in moments of comfort and convenience, but
where he stands at times of challenge and controversy.
<font size="-5"><br>
<br>
</font></font></dt>
<dd><font face="Arial,Helvetica"><i>Martin Luther King</i></font></dd>
</blockquote>
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