<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Hi Markus,<DIV><BR class="khtml-block-placeholder"></DIV><DIV><DIV><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Because I expected some changes (i.e., I assumed to get rid of some artifactual muscle activity),<SPAN class="Apple-converted-space"> </SPAN>now I can not judge whether these results are 'good' or 'bad'. Therefore, I would be interested in the 'slightly longer answer'.</DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV><DIV>When applying ICA to "real" data (i.e. where we do not really know everything about how the observed data are really generated) it is actually impossible to tell "objectively" whether removing components and then reconstructing the signal leads to "good" or "bad" results - it is basically a judgement call. Alternatively, you could use indirect arguments, e.g. related to improved ability to discriminate between two different conditions or something like that. The only way you can tell whether you successfully removed components from data is using synthetic data where you have a "ground truth".</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>(Philosophical / Methodological Aside: the same arguments apply to ANY mathematical or statistical method which involves numerical estimation of some model (always based on some assumptions) from data. Believe it or not, this would include nummerical integration techniques. The best you can ever do with numerical techniques is to understand their applicability criteria recognize their behaviour when these are criteria are not met. In the case of "real" data you must judge whether the data to satisfy the applicability criteria (big judgement), then brace yourself and jump ... that's as good as it ever gets, I am afraid :-)</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Furthermore, currently I do the ICA decomposition on all available segments (minus those with really excessive artifacts, which I took out before running ICA).<BR></DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV>Why do you remove these epochs? Do the signals saturate or is there excessive electrode(-cap) or subject movement in these?<BR><DIV><BR class="khtml-block-placeholder"></DIV><BR><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "> This means, my trials are a mixture of clearly contaminated as well as clearly uncontaminated trials. Because my main goal is to identify the eye and muscle artifacts, would it improve the detection of components reflecting artifacts if I do the ICA decomposition only on pre-identified artifactual trials? (My idea is that then the components reflecting artifacts would catch less 'true' brain activity. But perhaps I have a missconception here ...)</DIV></BLOCKQUOTE><DIV><BR class="khtml-block-placeholder"></DIV>The accuracy of the ICA decomposition relies fundamentally on the accuracy of the mixing matrix estimate A from which you form the de-mixing matrix (or vice versa). So if only some columns of A (e.g. artifact source sensor projections) are accurately estimated while the sensor projection estimates of brain activity are inaccurate (individually or as a subspace), then the de-mixing the data using W = inv(A) will not be fully successful in removing artifact activity from components reflecting the brain activity (subspace). In order to accurately estimate the sensor projections of ALL sources, the data needs to comprise example activity from ALL sources, i.e. BOTH artifact activity and brain activity.</DIV><DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>So since you need to estimate your brain activity (subspace) as accurately as your artifact sources, you should use as much of the data, i.e. contaminated and clean segments, as possible.</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>How many EEG channels do you have, by the way? I need to know in order to continue with the 'slightly longer answer'</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Regards,</DIV><DIV>Christian</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><BR><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Thank you very much for your help.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Best regards,</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Markus</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Christian Hesse schrieb:</DIV> <BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Hi Markus,</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">the short answer is: if (and only if, big if by the way) ICA correctly separates artifacts from brain activity, and you correctly identify the artifact components, removal of the artifact components from your data does not affect the time-frequency properties (including phase) of the other components (i.e. the rest of the data) if you project back to the sensor level. This is because ICA assumes a linear (instantaneous) mixing of statistically independent signals.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">I would just try it out for the<SPAN class="Apple-converted-space"> </SPAN>time being - if you get funny results (or things too good to be true), please get back in touch as there is also a slightly longer answer.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Hope this helps,</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Christian</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">On 23 Feb 2007, at 12:24, Markus Werkle-Bergner wrote:</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV> <BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Dear all,</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">in my studies, I'm investigating early preceptual binding (visual)</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">across the lifespan (i.e., I have data form children, younger and older</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">adults) with EEG measures. My main interest concerns changes in</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">gamma-power and measures of phase-synchronization in the gamma frequency range(e.g., phase-locking index, n:m (theta:gamma) phase synchronization).</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Currently<SPAN class="Apple-converted-space"> </SPAN>I use a 'semi-automatic' procedure for artifact rejection, i.e., I use thresholding in the time-domain (min/max in segment -/+ 100µV)to 'suggest' contaminated epochs. After that I visually inspect the data again for eye-blink and muscle activity, and completely reject the contaminated epochs.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">The problem with this procedure is that, especially in the older adults group, for many subjects only too few trials remain in the final sample.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Therefore, I thought I could use ICA for artifact correction (instead of complete rejection). After identification of the components that reflect muscle activity (and also other artifacts), I thought to recombine the remaining ICs and perform my analyses (power, PLI, n:m synchronization) on the recombined (cleaned data).</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Now my question(s): Is there any experience whether removing certain ICs</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">may change the phase spectrum, i.e. may this approach induce some</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">systematic bias? If there is a systematic bias, are different frequency</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">bands affected differentialy? Could anyone give me some references on</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">these issues?</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Any comments are very much appreciated.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Best regards,</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Markus</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">--<SPAN class="Apple-converted-space"> </SPAN></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">**************************************************************</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Markus Werkle-Bergner, Dipl. Psych.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Predoctoral Research Fellow</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Center for Lifespan Psychology</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Max Planck Institute for Human Development</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Lentzeallee 94, Room 211, D-14195 Berlin, Germany.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Phone: +49(0)30-82406-447 <SPAN class="Apple-converted-space"> </SPAN>Fax: +49(0)30-8249939</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">**************************************************************</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV> </BLOCKQUOTE><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">----------------------------------------------------------------------</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Christian Hesse, PhD, MIEEE</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">F.C. Donders Centre for Cognitive Neuroimaging P.O. Box 9101 NL-6500 HB Nijmegen The Netherlands</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Tel.: +31 (0)24 36 68293</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Fax: +31 (0)24 36 10989</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Email: c.hesse@fcdonders.ru.nl <<A href="mailto:c.hesse@fcdonders.ru.nl">mailto:c.hesse@fcdonders.ru.nl</A>></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Web: www.fcdonders.ru.nl <<A href="http://www.fcdonders.ru.nl">http://www.fcdonders.ru.nl</A>></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">----------------------------------------------------------------------</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV> </BLOCKQUOTE><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">--<SPAN class="Apple-converted-space"> </SPAN></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">**************************************************************</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Markus Werkle-Bergner, Dipl. Psych.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Predoctoral Research Fellow</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Center for Lifespan Psychology</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Max Planck Institute for Human Development</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Lentzeallee 94, Room 211, D-14195 Berlin, Germany.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Phone: +49(0)30-82406-447 <SPAN class="Apple-converted-space"> </SPAN>Fax: +49(0)30-8249939</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">**************************************************************</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV> </BLOCKQUOTE></DIV><BR><DIV> <SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><DIV>----------------------------------------------------------------------</DIV><DIV>Christian Hesse, PhD, MIEEE</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">F.C. Donders Centre for Cognitive Neuroimaging </DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">P.O. Box 9101 </DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">NL-6500 HB Nijmegen </DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">The Netherlands</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Tel.: +31 (0)24 36 68293</DIV><DIV>Fax: +31 (0)24 36 10989</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV>Email: <A href="mailto:c.hesse@fcdonders.ru.nl">c.hesse@fcdonders.ru.nl</A></DIV><DIV>Web: <A href="http://www.fcdonders.ru.nl">www.fcdonders.ru.nl</A></DIV><DIV>----------------------------------------------------------------------</DIV><DIV><BR class="khtml-block-placeholder"></DIV><DIV><BR class="khtml-block-placeholder"></DIV><SPAN class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "></SPAN><BR class="Apple-interchange-newline"></SPAN></SPAN></SPAN></SPAN></SPAN> </DIV><BR></DIV></BODY></HTML>