<html><head></head><body><div style="font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:small;"><div><div>Dear Makoto,</div></div><div> I think your criticisms are important and note that there are traveling waves in the EEG and also there is nonlinearity in the form of wave dispersion as noted by Nunez, 1981 and demonstrated in the paper that can be downloaded at this url (see Table IV):</div><div><br></div><div>http://www.appliedneuroscience.com/TWO-COMPARTMENTAL_MODEL_EEG_COHERENCE.pdf</div><div><br></div><div>It seems that your 3rd criticism does not recognize that ICA reconstruction of a new time series violates the "Reciprocity" theorem of Helmoltz and the "Lead Field" necessary for a valid inverse solution.</div><div><br></div><div>You mentioned a recent criticism on ICA that you stated is "technically invalid". I doubt that you are referring to the criticism about ICA reconstruction adulterating phase differences between EEG channels? The issue of ICA reconstruction and phase alteration is a settled issue based on math (not the separation of mixtures of phase or frequencies but rather the cross-spectrum at the same frequency at different locations) as well as multiple empirical demonstrations and tutorial demonstrations that anyone can verify for themselves. Also, I am copying from the Eelablist statements by yourself and five others agreeing that ICA reconstruction alters phase differences. </div><div><p class="ydpd4758496MsoNormal"><span style="font-size: 14pt;">“If you remove IC and
reconstruct channel EEG by back projecting the remaining ICs, of course it
changes channel EEG phase!” (Makoto Miyakoshi, Eeglablist ICA and signal phase
content, Sept. 16, 2014) </span></p>
<p class="ydpd4758496MsoNormal"><span style="font-size: 14pt;"> </span></p>
<div><span style="font-size: 14pt;">“The EEG
reconstruction after removing bad components/sources MAY change the phase value
of the signal at any electrode.” (M. Rezazadeh Eeglablist ICA and signal phase
content, Sept. 18, 2014).</span></div><div><span style="font-size: 14pt;"><br></span></div>
<p class="ydpd4758496MsoNormal"><span style="font-size: 14pt; font-family: "Times New Roman", serif;">“The
reconstructed data after removing spurious ICA components differs from the
original time series, and because of that there are phase differences.” (Arnaud
Delorme, </span><span style="font-size: 14pt;">Eeglablist
ICA misinformation, June 10, 2017).</span><span style="font-size: 14pt; font-family: "Times New Roman", serif;"></span></p>
<p class="ydpd4758496MsoNormal"><span style="font-size: 14pt;"> </span></p>
<p class="ydpd4758496MsoNormal"><span style="font-size: 14pt;"> </span><span style="font-size: 14pt; font-family: "Times New Roman", serif;">“</span><span style="font-size: 14pt; font-family: "Times New Roman", serif;">I first noticed the problem with phase distortion more than a
decade ago” (Robert Lawson, </span><span style="font-size: 14pt;">Eeglablist ICA misinformation, June 14, 2017).</span></p>
<p class="ydpd4758496MsoNormal"><span style="font-size: 14pt;"> </span></p>
<div><span style="font-size: 14pt; font-family: "Times New Roman", serif;">“I
think Bob is right that the relative phase will be changed by deleting 1 or 2
artifact components.” (Ramesh Srinivasan, </span><span style="font-size: 14pt;">Eeglablist ICA misinformation, June 14, 2017).</span></div></div><div><span style="font-size: 14pt;"><br></span></div><div><p class="ydpceab13d3MsoNormal"><span style="font-size: 14pt; font-family: "Times New Roman", serif;">“We
found phase distortions in the 8-10 Hz alfa band (greatest near the source of
artefact) but also on more remote electrodes such as occipital and also in
artefact free strokes of EEG.” (Georges Otte, </span><span style="font-size: 14pt;">Eeglablist ICA misinformation, June 15,
2017).</span></p></div><div>Best regards,</div><div><br></div><div>Robert</div><div><br></div><div id="ydpb3d79c09yahoo_quoted_1295088611" class="ydpb3d79c09yahoo_quoted"><div style="font-family:'Helvetica Neue', Helvetica, Arial, sans-serif;font-size:13px;color:#26282a;"><div>On Wednesday, July 26, 2017, 2:01:59 PM EDT, Makoto Miyakoshi <mmiyakoshi@ucsd.edu> wrote:</div><div><br></div><div><br></div><div><div id="ydpb3d79c09yiv4477574556"><div dir="ltr"><div>Dear List,</div><div><br></div><div>Recently there was a criticism against ICA on the list. Unfortunately it is technically invalid so I remained unsatisfied. Let me share real problems of the ICA model (Onton and Makeig 2006) to re-do it. This is a continued discussion from the one titled 'How phase is calculated in linear decomposition' and now this is my turn to criticize ICA!</div><div><br></div><div>As far as I know, there are three known limitations in ICA model.</div><div><ol><li>Spatial stationarity. I have seen a nice traveling waves in ECoG grid data during Joaquin Repela's presentation at SCCN. This clearly violates the assumptions of spatial stationarity in ICA.</li><li>Temporal stationarity. Shawn Hsu at SCCN presented time-series data of ICA model likelihood during drowsy driving task. Also, Jason Palmer's AMICA also demonstrated temporal changes in model likelihood. So one model per data does not fit the truth (unless the task has a strong control over a subject's cognitive and behavioral states).<br></li><li>Dipolar source model. Although most of ICA results are fit with dipole models, it seems ICA also returns (probably) non-point sources. When one fits a dipole model to such a non-point source, the location tend to end up with physiologically invalid depth (this is the most annoying thing about ICA today)</li></ol><div>I'd like to hear detailed criticism about these points. Note I saw these critical counterevidence in SCCN; we are not a boring ICA cult who have blind belief in it.</div><div><br></div><div>Nonetheless, ICA model has a critical merit. I named it <i>Independence-Dipolarity Identity (I-D Identity, or IDId)</i>. I-D Identity means that when ICA solves temporally problem, it also solves spatial problem at the same time <i>without using ANY spatial constraint</i>. Dipolarity can be thought of, in short, <i>biophysical origin-ness</i>. Hence I believe that this is evidence that ICA hits <i>some </i>physiological truth of EEG generation.</div><div><br></div><div>There could be multiple criticisms against the limitations of ICA model, but at the same time any criticism, at least so far, was NOT strong enough to deny <i>I-D Identity </i>of the ICA model<i>. </i>After all, because of this <i>I-D Identity</i>, I still advocate ICA (but similar dipolarity can be achieved by using very different approach, such as SOBI... so independence is not the only requirement to reach the biophysical validity. It's still a mystery to me.)</div><div><br></div><div>All models are wrong, but some are useful... but I want to go beyond this statement to reach the ground truth of EEG!</div></div><div><br></div><div>-- <br><div class="ydpb3d79c09yiv4477574556gmail_signature"><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div></div>
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