[FieldTrip] Covariance matrix, timelocking and lcmv beamformer

[Kaelasha Tyler]

Hi all,

I am raking through my script trying to sort out potential faults in my analysis.
One issue I have come across is whether ft_timelock analysis should be performed once, or twice when using lcmv method of beamformer.

The tutorial on lcmv beamfomer found here  http://fieldtrip.fcdonders.nl/tutorial/beamformer_lcmv?s[]=covariancewindow seems to indicate that time-locking is only performed once only in the analysis pipeline.

However, elsewhere on the FT site, I found the following advice:
"In order for the beamformer to work, we need the covariance between sensor pairs. This should be the covariance of (a particular latency window) of the averaged single trials. This is essentially different from the average covariance of the single trials. Therefore, we have to call timelockanalysis more than once: the first time we obtain the evoked field, and the second time we obtain the covariance matrix/ces at interesting latency/ies"

Which is correct?

I have been time locking twice: using data sets which were already time-locked using ft_timelockanalysis, and then time locking again, prior to using ft_sourceanalysis........... Wrong?

The phrase 'sanity check' comes up quite often on this list, and I absolutely understand! As always, any help is very much appreciated!!

Kaelasha






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