use of dipoles as spatial filters (for SEP)

Markus Bauer m.bauer at FIL.ION.UCL.AC.UK
Wed May 28 17:07:12 CEST 2008

> Did you consider trying out the beamforming algorithm with multiple
> dipoles as a source model?
> As opposed to the dipole-fitting (which pinv'es the concatenated
> leadfields), the beamformer actually tries to suppress contributions
> of the other guys (provided they are not too much correlated in time).
> Obviously, the suppression will be more robust against violations of
> the temporal uncorrelation-assumption, when the leadfield-columns are
> less correlated.
another reason why I didn't want to put the beamformer just into a
location to estimate the timecourse of the evoked field is that you
would have to calculate the covariance matrix-stepwise for each time
point (or at least over timeintervals, in a sliding fashion) - otherwise
the method is not legitimate - and I assume it will indeed substantially
distort the results if one just calculates one covariance matrix over
the whole (severely nonstationary) timeperiod where one wants to look at
the source-waveform.
this problem is more severe for evoked fields than in the frequency
doman cause of greater transients, not separated by frequency....

has anyone got more experience with this / investigated more in depth ?
my previous experience on this (with ordinary beamformers) wasn't that great


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