use of dipoles as spatial filters (for SEP)
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
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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