[Eeglablist] Re-referencing/rank/ICA

[Makoto Miyakoshi]

Dear Ivonne,

The smallest eigenvalue of 10^-20 is still regarded as 'independent' in
terms of rank() but for practical application of ICA the algorithm may
behave as if rank-deficiency is present. I believe I discussed this issue
with Jason Palmer last time. Isn't the current 'heuristic' minimum
eigenvalue cutoff something like 10^-8? You should be able to find it in
runica() function, if I remember correctly.

If you can specify data rank by using the pca option, that would be the
best to avoid this kind of problems.

So what you described seems correct, except

>  (deficient by 1 due to re-referencing)

A proper re-referencing should not reduce rank. See below.
https://sccn.ucsd.edu/wiki/Makoto's_preprocessing_pipeline#Why_should_we_add_zero-filled_channel_before_average_referencing.3F_.2803.2F04.2F2020_Updated.29


Makoto

On Tue, Jun 30, 2020 at 3:14 AM Ivonne Weyers <
ivonne.weyers at uni-osnabrueck.de> wrote:

> Dear all,
>
> I have a question regarding rank computation before ICA. So far, I have
> been using the built in MATLAB function rank(), but it has now returned
> weird results (as has been talked about here
> <https://sccn.ucsd.edu/pipermail/eeglablist/2012/004670.html>), which is
> why I would simply like to specify rank individually for each data set
> in the pca option. I would greatly appreciate it if someone could
> confirm my following reasoning for the rank adjustment.
>
> My data have been recorded from 28 channels with average reference, 27
> of which will enter the ICA (the monopolar EOG channel is excluded- yes,
> I could also include it). The 27 channels have been re-ferenced to
> average mastoids (TP9, TP10- is it correct to include these in the ICA
> at all?). For some subjects, a maximum of two channels have been
> interpolated.
>
> So my question is: if 27 channels enter the ICA, rank would be 26 for
> datasets without any interpolated channels (deficient by 1 due to
> re-referencing) and 26 - (number of interpolated channels) for those
> with interpolations?
>
> Thank you & best,
>
> Ivonne
>
> --
> Ivonne Weyers, M.A.
> Research Group Psycho- and Neurolinguistics
> Institute of Cognitive Science
> University of Osnabrück
> Room 50/104
> Wachsbleiche 27
> 49090 Osnabrück
> Germany
>
> Phone: +49 (0) 541-969-2247
> e-mail: ivonne.weyers at uni-osnabrueck.de
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