Thanks Christian. I will read the tr02 more detailedly
Xuelin
****************************************
Xuelin Cui
Department of Electrical Engineering
University of Hawaii-Manoa
Honolulu HI 96822
Tel: 1-808-349-0983
Email: [log in to unmask]
****************************************
----- Original Message -----
From: Christian Beckmann <[log in to unmask]>
Date: Tuesday, March 6, 2007 5:06 pm
Subject: Re: [FSL] some theoretical questions on MELODIC
To: [log in to unmask]
> Xuelin,
>
> all of these questions are readily answered in the technical
> report
> http://www.fmrib.ox.ac.uk/analysis/techrep/tr02cb1/tr02cb1.pdf
>
> > 1. Is PCA applied to the data before ICA is applied? (to
> decrease
> > the dimentionality)
> Yes, the maximum likelihood estimate is given by a rotated PCA
> solution (equation 5 in the TR)
>
> > 2. If PCA is applied as a preprocessing, where are those
> principal
> > components fed into?(put it in this way: After PCA applied, we
> have
> > a matrix E of some eigenvectors, is E same with X? where X=MS,
> X:
> > mixed information, M: mixing matrix, S: source)
> Nope, PCA uses the Eigenvectors of the data covariance matrix of
> X,
> see text after equation 5
>
> > 3: What criterion is used to extract those ICs by MELODIC?
> > (minimize the negentropy?)
> Approximations to neg-entropy, see text and equation 12
>
> > 4. What on earth are those ICs, which are extracted by MELODIC?
> Projections of the data which are maximally non-Gaussianity - see
> text and equation 12. You might find the section on 'uniqueness'
> interesting, too
>
> hope this helps
> Christian
>
> > Thanks a lot in advance
> >
> > Xuelin
> >
> > ****************************************
> > Xuelin Cui
> > Department of Electrical Engineering
> > University of Hawaii-Manoa
> > Honolulu HI 96822
> >
> > Tel: 1-808-349-0983
> > Email: [log in to unmask]
> > ****************************************
>
> --
> Christian F. Beckmann
> Oxford University Centre for Functional
> Magnetic Resonance Imaging of the Brain,
> John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
> Email: [log in to unmask] -
> http://www.fmrib.ox.ac.uk/~beckmann/ Phone: +44(0)1865 222551
> Fax: +44(0)1865 222717
>
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