<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Hi Chen<br>
<br>
These are inherent limitation of ICA.<br>
If you look at the mixing formular:<br>
x = As (with x mixed data, A mixing matrix and s sources)<br>
<br>
and you add a scaling of k<br>
<br>
x = B(k*s)<br>
<br>
you can match the scaling with B = (A/k)<br>
<br>
x = (A/k)(k*s)<br>
any arbitrary scaling factor k of the sources can be matched by the
mixing matrix. As both s and the mixing matrix are unknown, you will
never be able to recover the original amplitude. This of course is
also the case if you scale only a single source.<br>
<br>
For the Permutation of the signal it is similar, if you permute the
order of the sources, you can as well permute the order of the
Mixing matrix to match the mixed signal again. It is impossible to
do in this method. That is why usually ICA orders the components
with decreasing variance.<br>
<br>
If you want to read more about ICA I recommend:<br>
<a class="moz-txt-link-freetext" href="http://cis.legacy.ics.tkk.fi/aapo/papers/IJCNN99_tutorialweb/">http://cis.legacy.ics.tkk.fi/aapo/papers/IJCNN99_tutorialweb/</a><br>
Or directly the limitations:<br>
<a class="moz-txt-link-freetext" href="http://cis.legacy.ics.tkk.fi/aapo/papers/IJCNN99_tutorialweb/node4.html">http://cis.legacy.ics.tkk.fi/aapo/papers/IJCNN99_tutorialweb/node4.html</a><br>
<br>
Also interesting: Why gaussian variables are forbidden:<br>
<a class="moz-txt-link-freetext" href="http://cis.legacy.ics.tkk.fi/aapo/papers/IJCNN99_tutorialweb/node9.html">http://cis.legacy.ics.tkk.fi/aapo/papers/IJCNN99_tutorialweb/node9.html</a><br>
<br>
<br>
Hope this explanation helps.<br>
Best,<br>
Benedikt<br>
<br>
<div class="moz-cite-prefix">Am 06.02.2014 14:09, schrieb Chen Chen:<br>
</div>
<blockquote
cite="mid:CAPe_mmz=FdTt8L3yq=Y3sTzMaQ3rBQOO0OOLwD-tj3RrBUsrKQ@mail.gmail.com"
type="cite">
<div dir="ltr">Hi.
<div><br>
</div>
<div>I also have some questions about ICA, I wanna someone can
help.</div>
<div><br>
</div>
<div>I generated four orignal signals and mixed them with a
random matrix and add some noise, then I used ICA to remove
artifacts/noise and restore orignial signals, then I found,
after using ICA, the amplitude of orignial signals reduced and
the order of the orignial signals are changed.</div>
<div><br>
</div>
<div>How can I to sovle those two problems?</div>
<div><br>
</div>
<div>Thank you for your kindly responses.</div>
<div><br>
</div>
<div>CHEN</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">
On Wed, Jan 29, 2014 at 10:10 AM, Kristoffer Aberg <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:kc.aberg@gmail.com" target="_blank">kc.aberg@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>
<div>
<div>
<div>
<div>
<div>Hi,<br>
</div>
thanks for a wonderful toolbox!<br>
<br>
</div>
I will try to use ICA to remove blinks /
eye-movement / ECG artifacts, but i have some
questions i would be very happy if someone could
address:<br>
<br>
</div>
1. For the ICA decomposition, does it matter if the
electrode locations are correct? That is, would the
decomposition work even if the locations would be
completely randomized? I ask because i dont know
where to place the eye / ecg electrodes exactly.<br>
<br>
</div>
2. Is it a good idea to always include the eye / ecg
channels in the ICA decomposition? I ask because i
thought to decompose data based on scalp electrodes
only and then verify blink / pulse components by
comparing them to the eye / ecg channels. When should
i not include the eye / ecg channels in the ICA
decomposition?<br>
<br>
</div>
Thanks for your time and your responses!<br>
<br>
</div>
Kris<br>
</div>
<br>
_______________________________________________<br>
Eeglablist page: <a moz-do-not-send="true"
href="http://sccn.ucsd.edu/eeglab/eeglabmail.html"
target="_blank">http://sccn.ucsd.edu/eeglab/eeglabmail.html</a><br>
To unsubscribe, send an empty email to <a
moz-do-not-send="true"
href="mailto:eeglablist-unsubscribe@sccn.ucsd.edu">eeglablist-unsubscribe@sccn.ucsd.edu</a><br>
For digest mode, send an email with the subject "set digest
mime" to <a moz-do-not-send="true"
href="mailto:eeglablist-request@sccn.ucsd.edu">eeglablist-request@sccn.ucsd.edu</a><br>
</blockquote>
</div>
<br>
</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
Eeglablist page: <a class="moz-txt-link-freetext" href="http://sccn.ucsd.edu/eeglab/eeglabmail.html">http://sccn.ucsd.edu/eeglab/eeglabmail.html</a>
To unsubscribe, send an empty email to <a class="moz-txt-link-abbreviated" href="mailto:eeglablist-unsubscribe@sccn.ucsd.edu">eeglablist-unsubscribe@sccn.ucsd.edu</a>
For digest mode, send an email with the subject "set digest mime" to <a class="moz-txt-link-abbreviated" href="mailto:eeglablist-request@sccn.ucsd.edu">eeglablist-request@sccn.ucsd.edu</a></pre>
</blockquote>
<br>
</body>
</html>