[FieldTrip] Cross-Spectral Input to ft_eloreta
Nakhnikian, Alexander
Alexander_Nakhnikian at hms.harvard.edu
Wed Oct 29 18:19:51 CET 2014
Hello,
I'm trying to perform source analysis on an EEG data set using ft_eloreta. I've set up the analysis using the dipole and volume conduction models included in fieldtrip. I want to perform the analysis in frequency space, which means I need to enter a cross-spectral matrix for the variable Cf. The cross-spectral matrix returned by ft_freqanalysis doesn't work. ft_eloreta runs into trouble on line 163 "csd = dip.filter{i}*Cf*dip.filter{i}' " where Cf is the cross-spectral density matrix returned by ft_freqanalysis. This matrix has many rows and its number of columns is equal to the number of frequencies analyzed. The row number is (numChannels*(numChannels-1))^2/2, so it's assigning a row index to each pair-wise combination of channels, ignoring complex conjugate pairs and autospectra. The problem is that dip.filter{i} has dimensionality 3 x numChannels, which means Cf must be a numChannels x numChannels matrix to make the linear algebra work out. Is there a program in fieldtrip that returns a square cross-spectral density matrix for the frequencies of interest? Are there methods papers by Pascual-Marqui or others that deal with how to construct the cross-spectral matrix?
I am new both to fieldtrip and to eLORETA so any advice would be greatly appreciated.
Thanks in advance,
Alexander Nakhnikian
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