[Eeglablist] ICA Misinformation

Ramesh Srinivasan r.srinivasan at uci.edu
Wed Jun 14 11:11:35 PDT 2017

Hi All -

I think Bob is right that the relative phase will be changed by deleting 
1 or 2 artifact components.   Any artifact is broad-band and hence has 
components in each frequency bin.  When reconstructing the (in this 
example, 19) channels, the relative phases will change because some of 
the signal in each frequency bin has been removed when using only 17 or 
18 components.

The open question is whether the original relative phase or the 
ICA-corrected relative phase is the better estimate of the relative 
phase between the populations that contributed to each electrode.  It's 
not obvious to me to prefer the original relative phase with the 
artifact components.

Part of the problem for me (and I do use EEGLAB's ica) about identifying 
components as artifact in the ICA is that I don't think they contain 
just the artifact, they also contain some genuine brain activity that we 
are removing.  This bothers me, but I don't know a better solution.  
Even the case of the eye-movement artifact components is likely a mixture.

I'd like to see this discussion move away from algorithm to this harder 
question about artifact removal.


On 06/14/2017 10:43 AM, Robert Thatcher wrote:
> Iman,
>      Thank you for the information.  I could only find a power point 
> attachment of a simulation in your post.  I did not find a scientific 
> publication where you compared the phase differences changes between 
> an original EEG recording and a ICA reconstruction after removing one 
> or more components.   Please re-send your study.  Also please give the 
> citation to any of your publications or other’s publications where 
> phase differences were compared between the original EEG recording and 
> post ICA reconstruction.  It will be interesting to see if you found 
> similar changes like in the study by Montefusco-Siegmund et al or by 
> Georges Otte or even in the example pre vs post data files that you 
> can download from the internet.  I am assuming that you have 
> downloaded the EEG data and then used a JTFA like the Hilbert 
> transform or even the FFT cross-spectrum to prove to yourself that the 
> phase differences between the original and the ICA reconstruction have 
> not been preserved.
> As for the mathematics concerning reconstruction from a lower 
> dimensional matrix to a higher dimensional matrix where there are no 
> simple linear transforms I refer you to Taken’s theorem where “The 
> reconstruction preserves the properties of the dynamical system that 
> do not change under smooth coordinate changes, but it does not 
> preserve the geometric shape of structures in phase space.”  Also, in 
> standard differential geometry math courses the issue of lower 
> dimensional manifold mapping to higher dimensional manifolds shows a 
> loss of information in all cases.  Also, commonsense operates here 
> where one tries to reconstruct 19 channels of EEG using only 15 or 16 
> or 17 ICA components hence a loss of information.
> Finally, the brain is not a total chaotic organ.   As demonstrated by 
> many scientists (e.g., Nunez; Walter Freeman; Roberto-Pascual Marqui; 
> E. Roy John; Joel Lubar; etc) coherence and phase differences are well 
> behaved and highly reproducible within and between subjects. Coherence 
> and phase are dependent on the number and strength of connections 
> between groups of neurons.  Here is a URL to a study that tested Paul 
> Nunez’s two-compartmental model of Coherence and Phase Differences and 
> found that these measures vary as a function of distance and packing 
> density:
> http://www.appliedneuroscience.com/TWO-COMPARTMENTAL_MODEL_EEG_COHERENCE.pdf
> Here is a url to a study that used EEG LORETA correlations to 
> replicate Diffusion Tensor Imaging measures of connectivity in the brain:
> http://www.appliedneuroscience.com/DTI-ThatcherHumanBrainmapping.pdf
> Here is a url to a study that measured phase lock and phase shift 
> duration from birth to about 16 years of age in 458 and where phase 
> differences were stable and well behaved: 
> http://www.appliedneuroscience.com/PhaseresetDevelopment.pdf
> If you do a search of the National Library of Medicine database 
> (Pubmed) using the search terms “EEG coherence” you will find 2,874 
> citations.  There is huge consistency in this vast literature which 
> would be impossible if the brain was totally chaotic.
> Best regards,
> Robert
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