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Yes, I am reading that, and I am stuck on that. That's why I want to ask Christian, coz he wrote the report. Do you know when he will be back on Email again? Thanks 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: Tim Behrens <[log in to unmask]> Date: Monday, March 12, 2007 11:43 am Subject: Re: [FSL] some theoretical questions on MELODIC To: [log in to unmask] > Hi - > Christian is away at the moment I'm afraid. He is off email, but > did > you see that steve answered your questions as well as pointing you > to > the tech report. > > T > > > On 12 Mar 2007, at 21:36, Xuelin Cui wrote: > > > hi Steve: > > > > Thanks for reply > > > > But could you please forward my email to Christian? I am reading > > the technique report. Those questions are exactly the questions > on > > the technique report. > > > > Thanks > > > > 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: Steve Smith <[log in to unmask]> > > Date: Monday, March 12, 2007 7:34 am > > Subject: Re: [FSL] some theoretical questions on MELODIC > > To: [log in to unmask] > > > >> Hi, > >> > >> As well as Christian's main techrep, you should read the basic > >> intro > >> to ICA at: > >> http://www.fmrib.ox.ac.uk/analysis/techrep/tr01mj2/tr01mj2.pdf > >> > >> > >> On 12 Mar 2007, at 09:34, Xuelin Cui wrote: > >> > >>> hi Christian: > >>> > >>> I have a question on equation 5 in you technique report 2. > >>> > >>> Equation 5 seems to be the maximum likelihood estimation of > >> mixing > >>> matrix. It is: > >>> A_ml=U_q*(lamda_q-sigma^2*I)^1/2*Qt > >>> Is U_q the eigenvector matrix directly solved from the 2D fMRI > >> data > >>> by PCA? > >> > >> Nearly: it is the top q eigenvectors from the initial data PCA. > >> > >>> If so, should each of the column vector in U_q be orthogonal? > >> > >> Yes. > >> > >>> Also, I dont really figure out that where does the Q matrix come > >>> from. Since it is a rotational matrix, each column of it should > >> be > >>> orthogonal too, right? Why we need Q here? > >> > >> Q is the final ICA rotation within the space produced by the PCA. > >> WIthout Q you would just have PCA. > >> > >> Steve. > >> > >> > >>> > >>> 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] > >>> **************************************** > >>> > >>> ----- 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 > >>>> > >> > >> > >> ----------------------------------------------------------------- > --- > >> ---- > >> --- > >> Stephen M. Smith, Professor of Biomedical Engineering > >> Associate Director, Oxford University FMRIB Centre > >> > >> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK > >> +44 (0) 1865 222726 (fax 222717) > >> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve > >> ----------------------------------------------------------------- > --- > >> ---- > >> --- > >> >