<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>I agree with David's reasoning. You may find the following article to be of help as well in understanding the issues involved:</div><div><br></div><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Times; ">Dien, J., Khoe, W., & Mangun, G. R. (2007). Evaluation of PCA and ICA of simulated ERPs: Promax versus Infomax rotations. <i>Human Brain Mapping</i>, <span style="font: 13.0px 'Lucida Grande'">28</span><span style="font: 12.0px 'Lucida Grande'">(</span><span style="font: 13.0px 'Lucida Grande'">8</span>), <span style="font: 13.0px 'Lucida Grande'">742-763</span>.</div></div><div><br></div><div>Cheers!</div><div><br></div><div>Joe</div><br><div><div>On May 23, 2011, at 11:57 AM, David Groppe wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hi Odelia,<br> When you use ICA (or any other spatial filter) to correct for EEG<br>artifacts, you're going to distort your data some by removing true EEG<br>activity in addition to the artifact (for an explanation, see:<br><a href="http://www.cogsci.ucsd.edu/%7Edgroppe/PUBLICATIONS/GroppeCSO2008.pdf">http://www.cogsci.ucsd.edu/%7Edgroppe/PUBLICATIONS/GroppeCSO2008.pdf</a>).<br> So to minimize distortion, it would be better not to apply ICA<br>artifact correction to artifact-free data. However, if the frequency<br>of the artifact differs across experimental conditions, it could<br>confound your analysis. For example, I suspect people blink more<br>often to targets in an oddball experiment than standards. Thus if you<br>apply ICA only to blinky trials, you could find a difference between<br>the EEG response to standards and targets that simply reflects the<br>fact ICA removed more EEG activity in the target trials (i.e., it<br>wouldn't reflect a true difference in neural processing).<br> hope this helps,<br> -David<br><br>On Mon, May 23, 2011 at 1:44 AM, odelia nakar <<a href="mailto:odidodi@hotmail.com">odidodi@hotmail.com</a>> wrote:<br><blockquote type="cite">Hi all,<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I'm troubled by the fact that when I use ICA for blinks\eyes movements<br></blockquote><blockquote type="cite">removal, I remove the relevant components also from trials that do not<br></blockquote><blockquote type="cite">contain blinks\eyes movements. In order to avoid this bias we thought to<br></blockquote><blockquote type="cite">combine the data before ICA ("data" structure) with the data after ICA<br></blockquote><blockquote type="cite">("dataica" structure), only in specific trials, as follows:<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">datall=dataica;<br></blockquote><blockquote type="cite">datall.trial=data.trial;<br></blockquote><blockquote type="cite">datall.time=data.time;<br></blockquote><blockquote type="cite">blinks=[2 4 5 8 bla bla 156];<br></blockquote><blockquote type="cite">for ind=1:length(blinks)<br></blockquote><blockquote type="cite"> datall.trial{1,blinks(ind)}=dataica.trial{1,blinks(ind)};<br></blockquote><blockquote type="cite">end<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">To my first question: I just wanted to check that there is no problem with<br></blockquote><blockquote type="cite">that, or any reason not to use it.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Another issue- I use motor learning task, and I'm trying to understand what<br></blockquote><blockquote type="cite">happens through the process, in terms of power-frequency changes through the<br></blockquote><blockquote type="cite">process. How would you recommend that I'd use the ft_freqanalysis function?<br></blockquote><blockquote type="cite">What method to use (or what do I need to consider when choosing the method<br></blockquote><blockquote type="cite">field)?<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Thanks a lot,<br></blockquote><blockquote type="cite">Odelia.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">_______________________________________________<br></blockquote><blockquote type="cite">fieldtrip mailing list<br></blockquote><blockquote type="cite"><a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a><br></blockquote><blockquote type="cite"><a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a><br></blockquote><blockquote type="cite"><br></blockquote><br><br><br>-- <br>David Groppe, Ph.D.<br>Postdoctoral Researcher<br>Kutaslab<br>Dept. of Cognitive Science<br>University of California, San Diego<br><a href="http://www.cogsci.ucsd.edu/~dgroppe/">http://www.cogsci.ucsd.edu/~dgroppe/</a><br><br>_______________________________________________<br>fieldtrip mailing list<br>fieldtrip@donders.ru.nl<br>http://mailman.science.ru.nl/mailman/listinfo/fieldtrip<br></div></blockquote></div><br><div>
<div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Courier; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Courier; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; 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color: rgb(0, 0, 0); font-family: Courier; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Courier; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Courier; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Courier; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div><div><div><div><br>--------------------------------------------------------------------------------</div><div><br></div><div>Joseph Dien</div><div>E-mail: <a href="mailto:jdien07@mac.com">jdien07@mac.com</a></div><div>Phone: 301-226-8848</div><div>Fax: 301-226-8811</div><div><a href="http://homepage.mac.com/jdien07/">http://homepage.mac.com/jdien07/</a></div></div></div><br></div><div><br></div><div><br></div><br></div></div></span></div></span></div></span></div></span></div></span></div></span></div></span><br class="Apple-interchange-newline"></div><br class="Apple-interchange-newline"><br class="Apple-interchange-newline">
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