[Eeglablist] ICA Misinformation
rwthatcher2 at yahoo.com
Tue Jun 20 10:53:55 PDT 2017
1) On Phase Differences in the Originalvs the Delorme ICA Reconstruction: We can agree or disagreeabout whether or not some small eye movement artifact was in the hand selectionthat I did. But that misses the mainpoint here. That is the ICAreconstruction alters each and every data point in the entire record includingall artifact free portions no matter what one selects. For example, the record is 6 minutes and 51seconds = 411 seconds. The Mitsar samplerate was 250 samples per second = 102,750 data samples. Phase difference for each frequency band foreach and every one of the 102,750 data samples has been altered by your own ICAreconstruction in the EDF file that you emailed to me. Unless you were to sit next to me or if wedo a Team Viewer it is not possible for me to demonstrate this for all of thedata points and then create a power point for all of these data samples. However, I can show some exemplars, forexample, I have created two figures at 4 different time points (1 sec; 2:27 sec;42 sec & 5:49 sec) that you can download. You can extract each screen capture and expand them so that you can see thatthe exact same time points were selected and the Hilbert transform JTFA for the4 time points resulted in different phase differences in all channelcombinations with respect to O1 for all frequencies. The same is true no matter which channel isselected to compute the phase differences in degrees. The same is true also if one computes averages of the instantaneous phase differences or if one uses the FFT. Hereis the download URL:
2) On the WinEEG ICAReconstruction: I agree that havingaccess to ICA components themselves and the topography is critical inunderstanding exactly what the WinEEG software did. Unfortunately, I personally do not haveaccess to the WinEEG software. Clinician/Scientists in Australia use the WinEEG software and they werethe ones that expressed concern about phase difference distortion at a workshopin Adelaide and gave me the original and the WinEEG ICA eye movement correctedfiles in EDF format. They explainedthat they removed only one ICA component for eye movement before theyreconstructed a new time series. Atfirst, I was impressed because the eye movements were absent in thereconstructed time series. I then wasable to use JTFA (Hilbert transform) to compare the two edf files anddiscovered that all of the phase differences for all channels for allfrequencies had been altered by the ICA reconstruction including artifact freeperiods. I could demonstrate this by individualtime comparisons or averages of instantaneous phase differences or by theFFT. A user of WinEEG explained thatthey do not throw away the original raw digital data, however I was told that theybelieve that the ICA reconstructed times series is artifact free and thereforethey compute means and standard deviations for their normative database usingthe ICA reconstructed data and not the hand edited or artifact deleted originaldata samples like other commercial companies do. Your ICA reconstructed time series is actually less different than the original phase difference in comparison to the WinEEG ICA. Nonetheless, both your ICA reconstruction and the WinEEG reconstructions are significantly different than the original recording.
On Tuesday, June 20, 2017, 1:12:41 AM EDT, Arnaud Delorme <arno at ucsd.edu> wrote:
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.
On Jun 18, 2017, at 11:44 AM, Robert Thatcher <rwthatcher2 at yahoo.com> wrote:
<Pre-ICA-Hand Artifact free selections.edf>
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