beamforming and precomputed leadfields

Robert Oostenveld r.oostenveld at FCDONDERS.KUN.NL
Mon Aug 16 12:11:24 CEST 2004

Hi FieldTrippers,

Last weeks BIOMAG was fun, and I got quite some new ideas that I
already starten implementing. FieldTrip is definitely on the right
track and gained a lot of attention.

On the code level: I have made some modifications to the way that
leadfields are kept and/or precomputed. The old options of
SOURCANALYSIS are still supported, but there is also a new function
PRECOMPUTE_LEADFIELD. I suggest that you use the new function if you
want to perform resampling/randomization based source analysis and

Furthermore, we discovered a "feature" of the beamformer method that is
not so nice. Although it is not really a bug, but it might mess up your
sourceanalysis results if you are using multisphere headmodels as most
of us do. The problem has to do with the radial dipole component and
noise projection. If you are at the moment busy with sourceanalysis,
please contact me as soon as possible(!!) and I will explain it and
show you the workaround that is already implemented. For the rest of
you: I will explain it in more detail in this weeks thursday MEG

best regards,

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