<div dir="ltr"><div><span style="font-family:Calibri,sans-serif;font-size:14.666666984558105px"><font color="#000000">Dear Iman and Georges,</font></span></div><span style="color:rgb(31,73,125);font-family:Calibri,sans-serif;font-size:14.666666984558105px"><div><span style="color:rgb(31,73,125);font-family:Calibri,sans-serif;font-size:14.666666984558105px"><br></span></div>> So, if some sources are removed because of artifact removing procedure then the summation of the phase values of the  remainder sources may not be matched to the initial un-cleaned EEG.</span><br><div class="gmail_extra"><br></div><div class="gmail_extra">I agree with you Iman. Thank you.</div><div class="gmail_extra"><br></div><div class="gmail_extra"><span style="color:rgb(31,73,125);font-family:Calibri,sans-serif;font-size:14.666666984558105px">> As a result the component rejection procedure  MAY change the phase value/content at any given channel.</span><br></div><div class="gmail_extra"><br></div><div class="gmail_extra">It's not MAY, but SHOULD, because can you think of a situation where you keep the phase information identical before and after the IC rejection?</div><div class="gmail_extra"><br></div><div class="gmail_extra">Georges, here is another info that may help you.</div><div class="gmail_extra">EEG.data, EEG.icaweight, EEG.icasphere, and EEG.icainv are all real.</div><div class="gmail_extra"><br></div><div class="gmail_extra"><span style="color:rgb(31,73,125);font-family:Calibri,sans-serif;font-size:14.666666984558105px">> I would like to understand the mathematics and can only come up with this explanation but maybe I see it wrongly.</span><br></div><div class="gmail_extra"><br></div><div class="gmail_extra">Sorry I have no math skill to show why phases do not change, but here is my best explanation. There are two cases phases remain unchanged after component rejection.</div><div class="gmail_extra">1) rejected component is DC across time.</div><div class="gmail_extra">2) rejected component differs from the original signal only by a fixed scale across time.</div><div class="gmail_extra">However such component cannot be independent of other components.</div><div class="gmail_extra"><br></div><div class="gmail_extra">Makoto</div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Sep 18, 2014 at 12:54 PM, Iman M.Rezazadeh <span dir="ltr"><<a href="mailto:irezazadeh@ucdavis.edu" target="_blank">irezazadeh@ucdavis.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Hi, <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">The EEG reconstruction after removing bad components/sources MAY change the phase value of the signal at any electrode. Each source and its back projection into the channel space at any time point have individual phase value; however, the EEG phase value is a “summation†of all the phase values from each individual sources ( in other words, the EEG phase value at any given channel is the summation of phase values of each source/component reconstructed signal at that given channel). So, if some sources are removed because of artifact removing procedure then the summation of the phase values of the  remainder sources may not be matched to the initial un-cleaned EEG. <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Also, each source has a specific IC map ( spatial filter) so the effect of that source is distributed/propagated throughout all channels. The magnitude of the effect at any channel is proportional to the IC map value at that channel ( in EEGLAB: if the IC Map is dark red/blue, its effect is high; the greenish color means the effect is low) . So, by removing a source which may correspond to eye blink , the effect of that source/component  to other channels (other than ‘Fz’, for example)  will be also eliminated. As a result the component rejection procedure  MAY change the phase value/content at any given channel. <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Best<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Iman <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">============================================<u></u><u></u></span></p><p class="MsoNormal"><b><span style="font-size:10pt;font-family:'Arial Rounded MT Bold',sans-serif;color:rgb(112,48,160)">Iman M.Rezazadeh, Ph.D. , M.Sc., B.Sc.<u></u><u></u></span></b></p><p class="MsoNormal"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(31,73,125)">UCLA David Geffen School of Medicine</span><span style="color:rgb(31,73,125)"><u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(31,73,125)">Semel Institute for Neuroscience and Human Behavior</span><span style="color:rgb(31,73,125)"><u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(31,73,125)">760 Westwood Plaza, Ste 47-448</span><span style="color:rgb(31,73,125)"><u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10pt;font-family:Arial,sans-serif;color:rgb(31,73,125)">Los Angeles, CA 90095<u></u><u></u></span></p><p class="MsoNormal"><span style="color:rgb(31,73,125)"><a href="http://www.linkedin.com/pub/iman-m-rezazadeh/10/859/840/" target="_blank"><span style="color:rgb(5,99,193)">http://www.linkedin.com/pub/iman-m-rezazadeh/10/859/840/</span></a><u></u><u></u></span></p><p class="MsoNormal"><span style="color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><a name="1488a55edd105fc7__MailEndCompose"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></a></p><div><div style="border-style:solid none none;border-top-color:rgb(225,225,225);border-top-width:1pt;padding:3pt 0in 0in"><p class="MsoNormal"><b><span style="font-size:11pt;font-family:Calibri,sans-serif">From:</span></b><span style="font-size:11pt;font-family:Calibri,sans-serif"> <a href="mailto:eeglablist-bounces@sccn.ucsd.edu" target="_blank">eeglablist-bounces@sccn.ucsd.edu</a> [mailto:<a href="mailto:eeglablist-bounces@sccn.ucsd.edu" target="_blank">eeglablist-bounces@sccn.ucsd.edu</a>] <b>On Behalf Of </b>otte georges<br><b>Sent:</b> Thursday, September 18, 2014 9:26 AM<br><b>To:</b> <a href="mailto:mmiyakoshi@ucsd.edu" target="_blank">mmiyakoshi@ucsd.edu</a><br><b>Cc:</b> <a href="mailto:eeglablist@sccn.ucsd.edu" target="_blank">eeglablist@sccn.ucsd.edu</a><br><b>Subject:</b> Re: [Eeglablist] ICA and signal phase content<u></u><u></u></span></p></div></div><div><div class="h5"><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal"><span lang="NL-BE" style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Dear Makoto<u></u><u></u></span></p><p class="MsoNormal"><span lang="NL-BE" style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Thank You very much for the quick reply. I carefully checked the material You indicated in the link to the 2013 workshop (quite extensive but also  very interesting material) but could not find much specfic on the phase content (imaginary part) of the reconstructed EEG signals. In your mail You wrote to me  “of course it will change phaseâ€. Is that “of course†because of a regression process in reconstructing the time points from the remaining components (after the artefact components have been removed) or is there another reason ? I would like to understand the mathematics and can only come up with this explanation but maybe I see it wrongly. <u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">I read the article of Roberto Montefusco who concluded ( on both reaml EEG and simulated signals) that the phase changes after reconstructing the signal s are non stationary in time , location and frequency. For instanced he found major changes (after removing blink components ) at Fz, around 6 hz. But they were also present at other sensor locations and frequencies.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Phase was determined by using the Hilbert transform.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">All help and explanations would be very much appreciated.<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">-Sincerely<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Georges Otte<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u></u> <u></u></span></p><p class="MsoNormal"><b><span lang="FR" style="font-size:11pt;font-family:Calibri,sans-serif">De :</span></b><span lang="FR" style="font-size:11pt;font-family:Calibri,sans-serif"> Makoto Miyakoshi [<a href="mailto:mmiyakoshi@ucsd.edu" target="_blank">mailto:mmiyakoshi@ucsd.edu</a>] <br><b>Envoyé :</b> dinsdag 16 september 2014 4:09<br><b>À :</b> otte georges<br><b>Cc :</b> EEGLAB List<br><b>Objet :</b> Re: [Eeglablist] ICA and signal phase content<u></u><u></u></span></p><p class="MsoNormal"><span lang="NL-BE"><u></u> <u></u></span></p><div><p class="MsoNormal"><span lang="NL-BE">Dear Georges,<u></u><u></u></span></p><div><p class="MsoNormal"><span lang="NL-BE"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span lang="NL-BE">If you remove IC and reconstruct channel EEG by backprojecting the remaining ICs, of course it changes channel EEG phase!<u></u><u></u></span></p></div><div><p class="MsoNormal"><span lang="NL-BE"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span lang="NL-BE">Here is our EEGLAB workshop 2013 materials. You can find several powerpoint/pdf files that explains how ICA works on data cleaning.<u></u><u></u></span></p></div><div><p class="MsoNormal"><span lang="NL-BE"><a href="http://sccn.ucsd.edu/wiki/EEGLAB_2013_UCSD" target="_blank">http://sccn.ucsd.edu/wiki/EEGLAB_2013_UCSD</a><u></u><u></u></span></p></div><div><p class="MsoNormal"><span lang="NL-BE"><u></u> <u></u></span></p></div><div><p class="MsoNormal"><span lang="NL-BE">Makoto<u></u><u></u></span></p></div></div><div><p class="MsoNormal"><span lang="NL-BE"><u></u> <u></u></span></p><div><p class="MsoNormal"><span lang="NL-BE">On Sat, Sep 13, 2014 at 7:50 AM, otte georges <<a href="mailto:georges.otte@pandora.be" target="_blank">georges.otte@pandora.be</a>> wrote:<u></u><u></u></span></p><blockquote style="border-style:none none none solid;border-left-color:rgb(204,204,204);border-left-width:1pt;padding:0in 0in 0in 6pt;margin:5pt 0in 5pt 4.8pt"><div><div><p class="MsoNormal">Dear ICA experts<span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal"> <span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal">There is some discussion going on about the evidence that reconstructing an multichannel EEG after ICA decomposition and removing one or two artefact components could result in  scrambling the phase content (and coherence) of the reconstructed signals. Fi starting from a 19 ch EEG, removing two components with fi electrode pops and sweat artefacts , reconstructing the 19 ch EEG from 17 components (taking out the artefact containing ones)  without those artefacts. <span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal"> <span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal">Others say that this is not the case and that ICA respects the phase. However many authors (Zeman, Thatcher..) have published very convincing data to the contrary.<span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal"> <span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal">Any suggestions how to evaluate this ? Is it known from the algorithm what the reconstruction  will do to the phase content (imaginary part of the signal) ?<span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal"> <span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal">All help is very welcome<span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal"> <span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal">Sincerely<span lang="NL-BE"><u></u><u></u></span></p><p class="MsoNormal"><span style="color:rgb(136,136,136)"> </span><span lang="NL-BE" style="color:rgb(136,136,136)"><u></u><u></u></span></p><p class="MsoNormal"><span style="color:rgb(136,136,136)">Georges</span><span lang="NL-BE" style="color:rgb(136,136,136)"><u></u><u></u></span></p><p class="MsoNormal"><span style="color:rgb(136,136,136)"> </span><span lang="NL-BE" style="color:rgb(136,136,136)"><u></u><u></u></span></p><p class="MsoNormal"><span lang="NL-BE" style="color:rgb(136,136,136)"> <u></u><u></u></span></p></div></div><p class="MsoNormal"><span lang="NL-BE"><br>_______________________________________________<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><u></u><u></u></span></p></blockquote></div><p class="MsoNormal"><span lang="NL-BE"><br><br clear="all"><u></u><u></u></span></p><div><p class="MsoNormal"><span lang="NL-BE"><u></u> <u></u></span></p></div><p class="MsoNormal"><span lang="NL-BE">-- <u></u><u></u></span></p><div><p class="MsoNormal"><span lang="NL-BE">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<u></u><u></u></span></p></div></div></div></div></div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div>
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