Beamformer time course

Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Fri May 12 19:22:19 CEST 2006

Dear Marie,

On 10 May 2006, at 16:31, Marie Smith wrote:
> I have a question about the solution of a beam-former analysis and
> would appreciate any suggestions. Having used the beam-former
> technique to localize a region of interest for a specific time-
> frequency range, is there some function that can be implemented to
> compute the time course of activation for this roi?

For that you would use a time-domain beamformer, i.e. the lcmv
beamformer (cfg.method='lcmv' in sourceanalysis). That requires time-
domain data as input, so you should use timelockanalysis to compute
the covariance and the average. The covariance is used to construct
the beamformer filter and the average is projected through the
filter. If you want to project single-trial data through the filter,
you should keep the trials in timelockanalysis and use the option
cfg.singletrials='yes' in sourceanalysis (see its help).

If you are interested in a specific frequency band, you can use a
band-pass filter in timelockanalysis (the options for that are hidden
in the documentation, but they are the same as in preprocessing, e.g.
bpfilter='yes' and bpfreq=[low high]). It could also be that you want
to use a filter based on a narrow frequency band and use it to beam
the broad-band data. That is also possible, but not smoothly: you
have to do timelockanalysis twice (broadband and narrowband) and
replace the broadband covariance with the filtered narrowband
covariance. I hope this short explanation is enough.


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