[Eeglablist] ICA Misinformation

Stefan Debener stefan.debener at uni-oldenburg.de
Tue Jun 20 01:44:36 PDT 2017

Hi there,

It feels odd to me that an open source community spends time and effort 
into dealing with commercial software packages others apparently make 
good money with - by selling it to clinicians acquiring it in good 
faith. It should be the responsibility of commercial software developers 
to make sure their implementations are accurate, not the responsibility 
of this forum. Matter of fact, ICA has been so successful that many 
providers included it into their products. The few developers I know 
have done this with care, by validating their implementations against 
those distributed with EEGLAB. Does this hold for the developers of 
WinEEG as well? Who are the developers of WinEEG? How do they advise 
their "thousands of clinicians" on how to use ICA? Do they just offer a 
button to click or do they really care about their customers? Why are 
we, the experienced ICA users in this forum, blamed here?

Again, we should keep in mind the complexity of artifacts. Arno's reply 
nicely shows that there was a strong lateral eye movement artifact 
present at sec 3.25 Robert apparently ignored. When it comes to eye 
related artifacts, several sources may contribute even to a simple eye 
blink artifact as recorded with scalp EEG. While most of the blink may 
come from movement of the eyelids (causing the large monophasic 
deflection), some eye muscles need to contract as well to make the 
eyelids move, no doubt about it (all human behaviour requires muscle 
contraction, hence is generated by an electrial signature or "EEG 
artifact"). Sometimes the EMG initiation of a blink is visible after 
good ICA decompositions as a short, low amplitude high-frequency burst 
at the onset of the eye blink artifact (a hint of this "EMG" initiation 
of the blink is evident for instance in figure 5A of the CORRMAP 
reference paper (Fig 5A, black trace; in Viola et al., 2009, Clin 
Neurophysiology). At the same time the eyeballs rotate during a blink 
(interestingly in different direction, depending on whether the blink is 
voluntary or spontaneous! See 
https://www.ncbi.nlm.nih.gov/pubmed/15792897), and because the eyeballs 
are electrically charged as well this contribution can be expected to 
leave a trace in the EEG. Then of course we have lateral eye movements 
as in Roberts recording, and microsaccades and maybe some other 
processes like eyelid fluttering I am not well aware of... To avoid the 
"mess", some people may prefer an eyes closed EEG recording condition, 
aiming for artifact-free EEG. However, in many subjects one can clearly 
observe a slow rotation of the eye balls, which again will contribute an 
artifact in the EEG. I don't want to know how many "abnormal delta" 
diagnoses this may have caused...

More likely brain processes are more complex than EEG artifacts, but the 
complexity of artifacts should not be disregarded, as artifacts can 
easily result in misinterpretation. So, ignoring artifact is NOT the 
solution. I hope there is agreement here, at least.

In the hand of experienced users, ICA has been shown to be super useful 
in artifact correction, but far from perfect! Experienced users usually 
do not advertise ICA as the magic solution to every problem EEG comes 
with! Limitations are usually mentioned very clearly in discussion 
sections of methods papers, but of course authors cannot be blamed if 
readers do not read their whole paper. Robert's line of reasoning seems 
to be that because ICA "adulterates" the EEG signal in between blinks it 
does not work properly. In order to test this bold assumption it would 
be necessary to monitor all eye-related movements carefully (eye 
tracking & magnetic search coil) and simultaneously with EEG. Only then 
we would know what the eye blink generators are actually doing in 
between blinks, and how well, or how poorly, ICA captures and 
disentangles the different contributors. It seems unlikely to me that 
eye artifact generators are perfectly electrically silent in between 
blinks! In any case, such a multi-modal study should be done for MORE 
than 19 channels and for MORE than 1 min 41 secs per subject! It has 
been discussed frequently here and in several papers that ICA benefits 
from more channels and longer recording durations (and adequate 
preprocessing, etc...).

In my view, reasons for the confusion may be a poor software 
implementation, the insufficient consideration of EEG artifact 
complexity, and the relying on far from perfect recording conditions. 
Therefore it is not justified to make any bold statements on "ICA 
misinformation". Better would be to make proposals on how to adress the 
issue of ICA sensitivity/specificity in an open-minded way. This would 
require data to determine the sensitivty and specificity of ICA for 
removing eye artifact along with concurrent eye tracking and magnetic 
search coil recordings. As I mentioned before, and others have agreed, 
relying on the phase of the raw EEG trace is NOT a good gold standard. 
Even for high-SNR brain signals such as alpha activity some form of 
spatial filtering is necessary to optimize it (even a bipolar channel is 
a spatial filter!). The best approach would be to consult with SSVEP 
experts like Ramesh's group, and discuss an experiment where phase is 
known (or can be reasonably well estimated by the experimental 
manipulations). Maybe the company behind WinEEG, or the company seeling 
plenty of EEG software on appliedneuroscience.com, wants to sponsor such 
a multi-modal study?

Georges, I don't think we have a pessimistic view on the EEG, we enjoy 
the challenge that comes with a scientific view. Maybe good part of this 
discussion comes down to a scientific versus clinical view on EEG. If 
that's true, this would be sad news (for patients, actually!), but 
explain why a good part of the applied neurofeedback community seems so 
disconnected from the scientific EEG community. BTW, Georges, can you 
explain why your link www.zscoreloretanfb.be is a Belgian website 
selling Tommy Hilfiger outfit? I am not interested in Tommy Hilfiger 
outfit, I only want to know what zscoreloretanfb is.

Arno, I truly admire your patience!


Am 20.06.17 um 07:12 schrieb Arnaud Delorme:
> Dear Robert,
> 1) *On my ICA decomposition analysis on your data.* You have selected 
> a subset of the file where there is 1 minute and 41 second data of eye 
> free data. I was only able to select 40 seconds in the same file, and 
> I also showed that even in this short file, there was some residual 
> eye movements. Jason and Stefan agreed with me. This is the reason why 
> ICA components power spectrum over frontal channels (and frontal 
> channels only) was affected below 10 Hz frequency band in my data 
> analysis. So on my ICA decomposition, our disagreement comes from the 
> interpretation. You feel that the power we remove at low frequency in 
> frontal channel is not eye movement. In an attempt to convince you, I 
> have picked up a clean region from your EDF dataset, and did some 
> dipole localization at this latency. We see that in the clean data, 
> the best dipolar fit (with 2 symmetrical dipoles) ends up near the eye 
> balls with a residual variance of 6.9%. Hopefully this convinces you 
> that your data is not free of eye movement artifacts. If you are 
> willing to take a step further you might contemplate the idea that ICA 
> can remove this residual spurious activity.
> 2) *On the WinEEG ICA decomposition analysis.* It is critical for us 
> to see the scalp topography (and if possible continuous activity) of 
> the components the people at the Australia workshop selected. Without 
> this, it is not possible for us to comment on the cleaned data. I 
> agree with you that there was some phase distortion in alpha (visible 
> directly in the raw data in the first email you sent) and that this 
> should not be the case. However, without seing the ICA decomposition, 
> it is not possible for us to conclude as to wether people selected the 
> wrong ICA components or if the ICA decomposition implemented in this 
> software is buggy (ICA is not a simple algorithm and it is sensitive 
> to numerical imprecision and a lot of other parameters - a suboptimal 
> implementation could easily explain the WinEEG results). Also, you 
> seem to imply that the WinEEG people were running ICA on their data 
> then throwing away the raw data (which is why their ICA biased 
> neurofeedback database is useless for practical purposes). Is that 
> correct? One should never throw away the raw data. If they did throw 
> away the raw data, it is an indication that the WinEEG are not 
> rigorous in their approach and therefore might not have implemented 
> ICA in an optimal way. If it is not the case, one may easily 
> reconstruct the database of measures with or without ICA decomposition 
> (assuming ICA is done right which does not seem to be the case) then 
> assess data measure distoritions (power, phase index, etc…) in a 
> statistical fashion.
> Best wishes,
> Arno
> http://sccn.ucsd.edu/~arno/download/clean_edf_file_analysis2.pdf 
> <http://sccn.ucsd.edu/%7Earno/download/clean_edf_file_analysis2.pdf>
>> On Jun 18, 2017, at 11:44 AM, Robert Thatcher <rwthatcher2 at yahoo.com 
>> <mailto:rwthatcher2 at yahoo.com>> wrote:
>> <Pre-ICA-Hand Artifact free selections.edf>
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