[Eeglablist] ICA runs slowly and returns complex numbers

[Arnaud Delorme]

Dear Llana,

I do not have any reference for this. It is hard for me to understand why it would work well. Maybe Jason can step in and enlighten us.
Best,

Arno

On Dec 10, 2013, at 10:45 PM, Ilana Podlipsky <ilana.mlist at gmail.com> wrote:

> Dear Arno,
> 
> Thank you for your input.
> Can you elaborate why ICA on bipolar montage is not good? Can you give me a reference for this?
> From our experience it works quite well and separates well into reasonable components of signal and artifact.
> 
> Thank you
> Ilana
> 
> 
> On Tue, Nov 26, 2013 at 8:23 AM, Arnaud Delorme <arno at ucsd.edu> wrote:
> Dear Llana,
> 
> if ICA detects a rank of 57, then this is probably what you should use.
> ICA on bipolar montage will not be informative. ICA will attempt to model each channel reference so that common sources may be projected to all channels in a linear fashion.
> Best,
> 
> Arno
> 
> On Nov 24, 2013, at 3:18 AM, Ilana Podlipsky <ilana.mlist at gmail.com> wrote:
> 
>> Dear Arno,
>> 
>> Judging by the ICA output in Matlab the solution converges but very very slowly.
>> I use bipolar montage, each electrode is referenced to its neighbor. I use 64 electrodes recorded with one reference electrode and convert  it to 85 differential channels off line. ICA detects rank 57 but I changed it manually to 64 since this is the original number of channels, is that correct?
>> Meanwhile I tried binica on the same computer running Ubuntu, and it runs much faster (in 20 minutes). I would still like to resolve this issue because I'd prefer to work on Windows.
>> 
>> Thanks,
>> Ilana
>> 
>> 
>> 
>> On Wed, Nov 20, 2013 at 6:59 PM, Arnaud Delorme <arno at ucsd.edu> wrote:
>> Dear Ilana,
>> 
>> did your ICA solution converge (meaning that the weight difference decrease with time). This might be the issue.
>> Also, are you using average reference or linked mastoid. In this case, the data matrix rank is the number of channels minus 1. ICA tries to detect this automatically but sometimes fails. You then have to manually reduce the number of dimension by 1 when running ICA. If you have 64 channels, in the edit box for running ICA (where there is already 'extended', 1) you may add 'pca', 63.
>> 
>> Best,
>> 
>> Arno
>> 
>> On Nov 12, 2013, at 11:54 PM, Ilana Podlipsky <ilana.mlist at gmail.com> wrote:
>> 
>> > Hi All,
>> >
>> > Since I've recently changed my computer ICA in eeglab runs very very slowly and returns complex numbers.
>> > On my previous computer, on the same data I ran the same ICA  within an hour or two. On the new computer the same ICA takes more than 24 hours, After 512 steps it returns this message :
>> >
>> > Sorting components in descending order of mean projected variance ...
>> > Warning: Matrix is close to singular or badly scaled.
>> >          Results may be inaccurate. RCOND = 6.956943e-019.
>> >
>> > When I try to plot the ICA activations I don't see any traces and when I look into the EEG.icaact matrix I see only complex numbers. Tried both runica and binica.
>> > This has never happen to me with the old computer on the same dataset.
>> > Both the old and new computer run Win7 64bit, matlab 2008a and eeglab 12. The hardware of the computers is different.
>> >
>> > What could be the reason for this, and what can ?I do to solve this?
>> >
>> > Thanks for the help,
>> > Ilana
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>> 
> 
> 

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