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

[Mikołaj Magnuski]

Dear Caro,

The message you are seeing is because of the channel reconstruction you
performed.
As I just replied to one question on the list with text that is relevant to
your problem, I paste it here (with small modifications) for you:

By interpolating/reconstructing channels you are decreasing the linear
independency of the channels and this is where the rank-deficiency problem,
discussed several times on the list, emerges (you can learn some more on
this by searching the list archive). It is better to interpolate channels
after ICA. Actually - EEGlab produces a warning when interpolation is
performed on data without ICA weights.
 11 wrz 2013 23:10, "Caro Gattei" <carogattei at gmail.com> napisał(a):

> 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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