[Eeglablist] ICA and covariance matrix for CSP

[Bethel Osuagwu]

Thank you Makoto for your reply.
Reducing the number of channels stops the warning, but I did not check if the number of channels I eliminated equals the number of components removed. I will check if that is true although I think its true.
Also I have been told from FieldTrip that the problem can be solved by regularizing the (inverse)covariance matrix(adding some estimated noise to the diagonals) but am not sure exactly how much noise and the effect of adding this noise. 
Thanks
Bethel
________________________________________
From: Makoto Miyakoshi [mmiyakoshi at ucsd.edu]
Sent: 24 April 2013 21:14
To: Bethel Osuagwu
Cc:
Subject: Re: [Eeglablist] ICA and covariance matrix for CSP

Dear Bethel,

Sounds like it is because of reduced rank. Please try that you also discard the same number of channels after IC rejection to see what happens.

Makoto


2013/4/23 Bethel Osuagwu <b.osuagwu.1 at research.gla.ac.uk<mailto:b.osuagwu.1 at research.gla.ac.uk>>
Hi Everyone,

I have noticed that after using ICA to remove artifact in my signal, I can no longer compute the covariance matrices needed for common spatial pattern without matlab giving me warning regarding the accuracy of the estimated matrix. Indeed the estimated matrix is not accurate. This does not happen if I use only a small subset of my channels after removing noise with ICA.  If I do not use ICA at all the warning disappears.

I want to ask if anybody knows why ICA causes this issue and how I can fix it?

Thanks a lot.
Bethel Osuagwu
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--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego