[Eeglablist] ICA Misinformation

Jason Palmer japalmer29 at gmail.com
Sun Jun 18 14:44:03 PDT 2017


Robert,

 

Thanks for the clarification. So do I understand correctly that for the comparisons you are showing, you (1) manually selected non-blink segments and ran the “pre” measures, then (2) used EEGLAB to run ICA on the complete datasets, then (3) selected the (single) eye-blink component from the independent components (ICs) and removed it, then (4) again extracted the same previously manually selected non-blink segments from the (back-projected, ICA blink-free) EEG.data, and ran the measures again to produce the “delorme” results?

 

Focusing on the coherence results, it is surprising to me that removing only a frontally concentrated eye-blink component would significantly change the coherence in non-blink segments between say P4 and T6 electrodes, in non-blink, or even blink segments. I believe the impact of these findings would be greatly enhanced if you or your colleagues at Applied Neuroscience could produce (1) the ICA component maps that were rejected in this analysis, (2) the actual coherence values (not just the p-values), and (3) the datasets you used, including the original data and the manually selected blink-free data, so that the results could be reproduced and verified by others. Apologies again if you have been over this previously in the discussion.

 

One of the central motivations of the ICA approach is that channel level coherence is fundamentally misleading since brain sources in a particular area may project widely across most or all electrodes, so that coherence between electrodes at different channel locations is not a valid measure of coherence between brain regions corresponding to those locations. Non-zero phase lag is not as susceptible to this criticism as single sources will project with zero phase-lag, though still the attribution of the “source” of the activity to the brain region below the channel is suspect. However, that said, ICA advocates would not expect the channel coherence that exists between non-frontal channels to be significantly altered by the removal of an eye-blink IC, and, particularly given the consternation created in the clinical field, it would be of great importance to determine the cause.

 

Thanks again, best,

Jason

 

P.S. Happy Father’s Day

 

 

From: Robert Thatcher [mailto:rwthatcher2 at yahoo.com] 
Sent: Monday, June 19, 2017 5:34 AM
To: japalmer at ucsd.edu
Cc: 'Iman Mohammad-Rezazadeh'; 'Ramesh Srinivasan'; 'Stefan Debener'; 'Arnaud Delorme'; 'eeglablist'; pnunez at tulane.edu; 'Georges Otte'
Subject: Re: RE: [Eeglablist] ICA Misinformation

 

Jason,

   Thank you again.

 

You stated: "When you say “artfact free data” you are not referring to selected time periods without eye-blinks are you? "

 

Reply: Yes that is correct.  Most uses of QEEG software are very experienced in EEG having measured sometimes hundreds of patients and they simply manually delete eye movements or other artifact and some manually only select sections of the EEG record that do not have artifact of any type.  For example, with a 5 minute recording they typically try to select at least 2 minutes of artifact free data.  Highly reliabile cross-validated results are obtained with multiple but different artifact free selections including high cross-validation and reliability across software platforms, for example, NxLink vs EEGpro or vs NeuroGuide or NeuroRep or Lexicor or Cadwell, etc.    Some also first select a 10 second sample of artifact free and then based on peak-to-peak amplitude select more artifact free segments.  Eye movement is generated by millivolt sources between the cornea and the retina with a clear voltage gradient as a function of distance and is easy to see and also usually many times larger than the artifact free EEG.

 

You stated: "the significant difference is largely over the frontal electrodes, where eye-blinks are influential."

 

Reply: This is not correct.  All channels and frequencies and metrics are different because all of the individual data points in the artifact free part of the record have been altered.  I am attaching examples of the statistics of the coherence and phase differences that show the adulteration is widespread in frequency and location.

 

You stated: "I would very much appreciate reference to some clinically relevant application beyond stating a simple difference in many measures."

 

Reply: The 1st  clinical group to use ICA reconstruction that I am aware of was the Brain Resource Center in Australia.   I became aware of a problem during a court trial in 2010 where I was an expert witness and because of totally different results compred to NxLink, NeuroRep and Skill software the court disallowed the ICA reconstruction in that case.   Around 2012 WinEEG implemented ICA reconstruction for clinical purposes and shortly thereafter various users and clinicians began to question the ICA reconstruction and asking me questions about it.   The clinical application of QEEG involves linking the patient's symptoms to dysregulation in brain networks related to the symptoms, for example, visual problems and the visual cortex, motor movement problems and the sensory motor cortex or MRI confirmed frontal lobe loss of brain tissue and the QEEG measured in the frontal regions and the connectivity to other parts of the brain, etc.  After ICA reconstruction it is diffcult to link the EEG to the patient's symptoms or the MRI, etc.

 

 

You stated: "Also, are you claiming that eye-blinks should not be removed by any method?"

 

Reply: Absolutely not.  I am simply asking why use ICA reconstruction given that the artifact free parts of the record have been altered when other artifact deletion methods are well established over the last 50 years that are used with very high reliability and cross-validation and do not alter the artifact free parts of the record?

 

Thank you again and best regards,

 

Robert

 

 

 

On Sunday, June 18, 2017, 3:53:11 PM EDT, Jason Palmer <japalmer29 at gmail.com> wrote:

 

 

Dear Robert,

 

Thank you for your reply and data. I think it would be very helpful if you could explain how the data you are presenting is used by clinicians and why it causes them great concern. I do not find it surprising at all that measures are significantly changed when eye-blinks are removed. When you say “artfact free data” you are not referring to selected time periods without eye-blinks are you? If you are comparing periods containing eye-blinks to data reconstructed with eye-blinks removed, then clearly the measures will be different. The simple fact that measures are different is not surprising. As far as I am able to interpret the figures, the significant difference is largely over the frontal electrodes, where eye-blinks are influential. Again, that is entirely what one would expect. If removing eye-blinks from data did NOT cause any change in measures, then THAT would be surprising and seem to argue that removing eye-blinks is unnecessary at all.

 

Again, I would very much appreciate reference to some clinically relevant application beyond stating a simple difference in many measures. For example, if there were a study of beta activity in orbito-frontal cortex, and clinicians were finding a significant difference in populations at the channel level, perhaps using a more traditional eye-blink removal technique, but not using the ICA based eye-blink removal, then I think that would be very compelling.

 

Also, are you claiming that eye-blinks should not be removed by any method? That would seem to invite the objection that the results in a study of frontal regions, say, are potentially conflated by eye-blinks. If you are claiming that it is only the ICA method of eye-blink removal that causes the unacceptable data distortion, do you have a similar set of plots using a more traditional eye-blink removal method that do not show significant differences in the measures you presented?

 

Are the “Delorme” plots using EEGLAB instead of WinEEG? (Apologies if you have already discussed this previously.)

 

Thanks, best,

Jason

 

 

 

From: Robert Thatcher [mailto:rwthatcher2 at yahoo.com] 
Sent: Monday, June 19, 2017 4:17 AM
To: Jason Palmer
Cc: Iman Mohammad-Rezazadeh; Ramesh Srinivasan; Stefan Debener; Arnaud Delorme; eeglablist; pnunez at tulane.edu; Georges Otte
Subject: Re: [Eeglablist] ICA Misinformation

 

Jason,

    Thank you and I understand your strong feelings since you stated:  " I have not seen any convincing evidence that there is a clinically significant alteration caused by judicious use of ICA for artifact removal and data reconstruction"

   

 

 I am attaching a .zip file that shows about 75% to 90% of EEG metrics are statistically significantly different from the original EEG with eye movement deleted vs post ICA reconstruction.  Also, there are edf files of the original, and post ICA by clinicians in Australia (they used WinEEG) and the Post ICA by Arno.   As you can see they are all different from each other.

 

I am not the person who first noticed the adulteration of artifact free segments of the original EEG by ICA reconstruction.   Our company has over 3,000 clinicians using our software and it the users of our software who complain about the adulteration.  You and Arno are going to have to convince these hunderds of hard working clinicians that ICA does not distort the original EEG.   Clinicians are seeing patients with serious clinical disorders and this is not an issue that can be dismissed because you have not seen any evidence of adulteration and also because you have not taken the time to compare the original EEG recording after only analysing parts of the record with no eye movement to the same artifact free part of the record after ICA reconstruction.  If there was no adulteration then the digital values and phase and coherence would be identical.  Instead they are statistically different at P < 0.0001 in well over half of the comparsions.

 

WinEEG was first incorporated aroun 1998 and has over 5,000 clinicians that use their software ICA.   I recommend that you do an internet search for WinEEG to learn more.  This is not a trivial number of individuals who are having problems achieving stable assessments of their patients and who also complain about ICA reconstruction.

 

Respectfully,

 

Robert

 

 

On Sunday, June 18, 2017, 3:04:17 PM EDT, Jason Palmer <japalmer29 at gmail.com> wrote:

 

 

Hi Robert, 

 

The statement that "the jury is in and the verdict is Do Not Use ICA Reconstruction" sounds incredibly presumptuous and unjustified. I believe Arnaud has admirably refuted your alpha example and I have not seen any convincing evidence that there is a clinically significant alteration caused by judicious use of ICA for artifact removal and data reconstruction. Your claim that ICA reconstruction is decoupled from the brain, etc., is incorrect. The back-projection of the source data, after components like eye-blinks are removed, is entirely "coupled" to the brain and the original data recording. The reconstruction / back-projection is NOT based on z-score ICA component activations, but on the simply linearly transform based activations. It is simply not true that the ICA reconstructed data is divorced from the brain. The same phase and amplitude relationships and generating source locations will exist in the reconstructed channel data without artifacts like eye-blinks, line-noise, scalp muscles, etc. as exist in the original channel data.

 

The notion that it is wrong to use ICA for eye-blink removal because "every data point is changed" again does not sound like a reasonable statement. It is equally correct to say that the EM potential added to the EEG by eye-blinks themselves "change the data". There are several papers that demonstrate the superiority of ICA based eye-blink removal over the "many other methods" that exist, and thus it is incorrect to say that there is no justification to use ICA over other methods. If you turned your polemic against other methods of eye-blink removal, such as regression, I have no doubt that you would find similar or greater grounds for objection based on you stated reasons.

 

I have not used or heard of WinEEG. Citing a specific implementation as a basis for rejection of a method is again unfair.

 

I hope that before issuing general method censure, you will take the time to use the freely available EEGLAB software to demonstrate any let alone a clinically important example of ICA 
"phase distortion". Your extreme warnings about the "phase distortion" caused by ICA do not seem to be founded in a correct understanding of the way ICA works. It is a linear transformation, creating a simple linear decomposition of the signal into constituent components, including eye-blinks. Theorems from differential geometry are irrelevant. Reconstructing the data with the eye-blink component left out will NOT cause any phase distortion in ICA. The statement that "every data point is changed" is not scientifically compelling. ICA is INCREDIBLY USEFUL FOR ARTIFACT REJECTION AND DATA RECONSTRUCTION as demonstrated by countless published papers. Cautioning against the use of automatic component rejection is one thing, but the issuance of general injunctions against using ICA for data reconstruction at all is clearly unwarranted. 

 

I apologize for the strident tone of this email, but there seems to be a somewhat cavalier and patronizing tone with a predetermined conclusion in the arguments I have seen made against the use of ICA thus far, and the polite responses of Arnaud, Iman, Stefan, et al. compared to your forceful, and I believe as yet unjustified by compelling evidence beyond what has been already addressed by Arnaud, or hearsay and reference to people from a particular community largely influenced by yourself, will likely be misleading to the general reader of this discussion.

 

The "jury" may be in, but the verdict is not as you claim. There are some who hold out a "guilty" verdict against ICA, but they are far from a majority.

 

Regards,

Jason Palmer

 

P.S. The yahoo.com email you are using is consistently being put in "spam" by gmail, and not even showing up in my Microsoft Outlook mail (even in junk mail). Gmail claims that the address "fails yahoo.com's required tests for authentication". It would be very helpful and appreciated for this discussion, assuming there is no ready solution to the yahoo.com issue, if you might consider using an alternative email.

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