[Eeglablist] ICA Misinformation

Robert Thatcher rwthatcher2 at yahoo.com
Wed Jun 14 14:54:43 PDT 2017


Hi Arnaud,    Thank you again.   This is a useful discussion and it is important to continue to explore.  There seems to be mismatch between empirical observation and theory (not uncommon in science).  I do not have or use EEGlab however if you were to attach the .edf files of the raw digital data, one edf of before and one after then myself and others will be able to compute the Hilbert transform and other JTFA and FFT methods to examine any changes in phase difference between pairs of channels.  Visual examination is not sufficient.  I noticed that single instances of time for some channels appear unchanged in some frequency bands using the Hilbert transform.  The average of changes in phase difference between channels shows larger changes the greater the number of samples in the average.  
The Australian data was analyzed by two scientists/clinicians in the audience of a workshop that I was doing in 2014 and they are the ones that did the ICA component selection using commercial WinEEG software and not me.  They demonstrated what they did and they only removed one ICA component for eye movement.  You can see that the ICA performed quite well and successfully remove the eye movement.  However, more subtle changes in wave shape are visible in the raw digital EEG and it is likely that the accumulation of these changes in phase difference between channels are what caused the large average changes.   I am busy at the moment with swLORETA and other things and can in the future explore the changes.  If you attach your ICA corrected data files as edf files then we can examine them and begin to find ways to improve ICA or find corrections, etc.  Once I get more free of current demands and burdens then I will activate the EEGlab software and also I can activate Neuroguide on your and others computers so that we can explore this important issue further.
You are welcome to download NeuroGuide and install and launch and then paste the key A into an email to me.  I have posted a tutorial on our webpage but I can create a better tutorial to reduce the learning curve.  Similarly when I am able to concentrate on EEGlab then you can tutor me to reduce my learning curve.  Here is a url to the download webpage:http://www.appliedneuroscience.com/Download_NeuroGuide.htm

At the end of the day together lets find ways to use the full power of ICA to explore network dynamics which is my favorite topic and also one that future science depends on.
Best regards,
Robert

On Wednesday, June 14, 2017, 4:40:43 PM EDT, Arnaud Delorme <arno at ucsd.edu> wrote:

Dear Robert,
There does seem to be a phase difference in your powerpoint. However, it is important to know which ICA component you removed to understand why this is the case. Are you sure these were artifactual components? Removing brain components may alter the phase of the signal recorded on the scalp (it would be as if you were removing from the scalp signal the contribution of a brain area). Without that information, it is not possible to figure out the origin of the phase difference. 
This seems to be the same data you shared yesterday. I have looked at it. Black is before ICA and red after removing the 2 eye components. You can see that there is no phase shift at 102.43 second after I remove the two artifactual ICA components. I have provided the code in my email yesterday if you want to reproduce this result in EEGLAB.
Best wishes,
Arno


On Jun 14, 2017, at 11:14 AM, Robert Thatcher <rwthatcher2 at yahoo.com> wrote:
<Example of Phase Differences at   1min & 46 seconds.pptx>

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