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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoPlainText>Dear Max, et al,<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>These two components are most likely slightly different—the thing to plot would be the difference of the maps and of the activations (after reversing the polarity/sign of one of the components—multiply the map and activation by -1). The difference should not be exactly zero.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>As Guillaume said, ICA can produce these "dependent subspaces" even if the data is really full rank. These components will have mutual information with each other, but should have close to 0 MI with other components.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Also, the time courses might be slightly time delayed, resulting in instantaneous independence, but delayed dependence. A movie of the backprojected sum of the maps might indicate a dynamic "wiggle" in the map (potential distribution), which would result from the dynamic (non-static spatial potential distribution) nature of the generating source.<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Best,<o:p></o:p></p><p class=MsoPlainText>Jason<o:p></o:p></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'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> eeglablist-bounces@sccn.ucsd.edu [mailto:eeglablist-bounces@sccn.ucsd.edu] <b>On Behalf Of </b>Maximilien Chaumon<br><b>Sent:</b> Wednesday, August 24, 2011 2:19 AM<br><b>To:</b> Guillaume Rousselet<br><b>Cc:</b> eeglablist@sccn.ucsd.edu<br><b>Subject:</b> Re: [Eeglablist] ICs with identical topographies<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Hi Guillaume,<br><br>Well, it makes sense to my intuitive understanding...<br>The two components don't cancel each other, but then sum up, more or less. Does that mean that I could somehow treat them as "one" component? <br>I get your point with this superclean dataset example. And it also makes sense with the other answers I got, with the rank of my data being not exactly as high as I expect it to be. Now I need to understand why/how some of my channels turn out to be linearly related...<br><br>Thanks,<br>Mx<o:p></o:p></p><div><p class=MsoNormal>2011/8/24 Guillaume Rousselet <<a href="mailto:Guillaume.Rousselet@psy.gla.ac.uk">Guillaume.Rousselet@psy.gla.ac.uk</a>><o:p></o:p></p><div><div><p class=MsoNormal>Hey Max,<o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>your components don't cancel one another. In your example, the topographies and the time courses have opposite signs, so if you multiply one by the other, your two components are essentially the same.<o:p></o:p></p></div><div><p class=MsoNormal>ICA returns maximally independent components, and therefore can still be correlated. The correlation can be quantified using the mutual information plugin, which I use to confirm my own judgement about component similarity when I look for eye blink ICs.<o:p></o:p></p></div><div><p class=MsoNormal>Imagine you have an absolutely clean signal, with only highly reliable evoked activity and no noise at all. In that case you would expect to get n times your number of electrodes the same component. In my experience, cleaner datasets tend to have more correlated - almost identical - ICs.<o:p></o:p></p></div><div><p class=MsoNormal>Makes sense?<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Best,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Guillaume<o:p></o:p></p></div><div><div><div><div><div><div><p class=MsoNormal style='margin-bottom:13.5pt'><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'><br>************************************************************************************<br>Guillaume A. Rousselet, Ph.D., senior lecturer & deputy post-graduate convenor<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Centre for Cognitive Neuroimaging (CCNi)<br>Institute of Neuroscience and Psychology <o:p></o:p></span></p></div><div><div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>College of Medical, Veterinary and Life Sciences<o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>University of Glasgow<br>58 Hillhead Street<br>G12 8QB<o:p></o:p></span></p></div></div></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'><o:p> </o:p></span></p></div><div><div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'><a href="http://www.psy.gla.ac.uk/staff/index.php?id=GAR01" target="_blank">http://www.psy.gla.ac.uk/staff/index.php?id=GAR01</a><o:p></o:p></span></p></div></div><div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'><o:p> </o:p></span></p></div></div></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Email: <a href="mailto:Guillaume.Rousselet@glasgow.ac.uk" target="_blank">Guillaume.Rousselet@glasgow.ac.uk</a><o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Fax. <a href="tel:%2B44%20%280%29141%20330%204606" target="_blank">+44 (0)141 330 4606</a><o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Tel. <a href="tel:%2B44%20%280%29141%20330%C2%A06652" target="_blank">+44 (0)141 330 6652</a><o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Cell <a href="tel:%2B44%20%280%29791%20779%207833" target="_blank">+44 (0)791 779 7833</a><o:p></o:p></span></p></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'><o:p> </o:p></span></p></div><div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>The University of Glasgow, charity number SC004401<o:p></o:p></span></p></div></div><div><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>************************************************************************************<o:p></o:p></span></p></div></div></div></div></div></div><p class=MsoNormal><o:p> </o:p></p></div><div><div><div><p class=MsoNormal>On 23 Aug 2011, at 15:24, Maximilien Chaumon wrote:<o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><div><p class=MsoNormal>Hi eeglabbers,<br><br>I sometimes get ICs with extremely similar topographies and time courses, like on <a href="http://oszilla.hgs.hu-berlin.de/public/Similar_ICs.PNG" target="_blank">this slide</a>.<br>I know that ICA returns independent components.<br>Does that not mean that they should not look the same?<br>I know the components are independent in a statistical sense, which is not the same as uncorrelated, but still. I'm a bit surprised. What do these two components mean if they cancel one another? well, do they?<br><br>Sorry if my question is naive, but what is happening?<br><br>The data is <a href="http://oszilla.hgs.hu-berlin.de/public/Similar_ICs.mat" target="_blank">here</a>.<br><br>Best,<br>Max<o:p></o:p></p></div></div><div><p class=MsoNormal>_______________________________________________<br>Eeglablist page: <a 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 href="mailto:eeglablist-unsubscribe@sccn.ucsd.edu" target="_blank">eeglablist-unsubscribe@sccn.ucsd.edu</a><br>For digest mode, send an email with the subject "set digest mime" to <a href="mailto:eeglablist-request@sccn.ucsd.edu" target="_blank">eeglablist-request@sccn.ucsd.edu</a><o:p></o:p></p></div></blockquote></div><p class=MsoNormal><o:p> </o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p></div></body></html>