[Eeglablist] Problem running ICA: rank of data lower than the number of input data channels

Caro Gattei carogattei at gmail.com
Thu Sep 12 08:17:43 PDT 2013


Many thanks for your responses, Makoto and Mikolaj!
They were very helpful.

Best regards,
Caro


2013/9/11 Makoto Miyakoshi <mmiyakoshi at ucsd.edu>

> Dear Caro,
>
> > I should mention that we had to reconstruct two channels before the
> analysis due to equipment problems. Could that account for part of the
> problem?
>
> Yes that's it.
>
> > I must also insist on the fact that even when chennels were
> reconstructed for other subjects, I son-t always get the message.
>
> Because it also depends on data quality. From my experience I would expect
> that if you have a lot of EMGs you would see that message more often.
>
> > A second question I have is, should I edit the rank to 30 or should I
> just run it with 28 components? how would that affect my data?
>
> Just run it with 28 components. Using PCA should be fine after channel
> interpolation, but why don't you go simple if you can.
>
> I have seen and experienced rank issues. I would avoid it whenever I can.
> Try matlab function rank on your fully processed data. It often returns
> much less number than your number of channels.
>
> Makoto
>
>
> 2013/9/11 Caro Gattei <carogattei at gmail.com>
>
>> Dear all,
>>
>> I am currently running an experiment with a 32 channel equipment (30+
>> ext) and when I try to run ICA in specific subjects I get a message saying
>> that "EEGLAB has detected that the rank of your data matrix is lower the
>> number of input data channels. This might be because you are including a
>> reference channel or because you are running a second ICA decomposition.
>> The proposed dimension for ICA is 28 (out of 30 channels) rana computation
>> may be innacurate so you may edit this number below. If you do not
>> understand, simply press OK"
>>
>> I found an explanation for the error message on the eegab list that said
>> that the ranking could be reduced de to low-pass filtering (being that I do
>> not have a reference  channel and hand't run ICA previously:
>>  http://sccn.ucsd.edu/pipermail/eeglablist/2012/005110.html
>>
>> However, I get the same message when I try to run ICA with raw data.
>>
>> I should mention that we had to reconstruct two channels before the
>> analysis due to equipment problems. Could that account for part of the
>> problem?
>>
>> I must also insist on the fact that even when chennels were reconstructed
>> for other subjects, I son-t always get the message.
>>
>> A second question I have is, should I edit the rank to 30 or should I
>> just run it with 28 components? how would that affect my data?
>>
>> Best regards,
>>
>> Caro
>>
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>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>
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