[FieldTrip] covariance computation from ft_timelockanalysis

[jan-mathijs schoffelen]

Hi Luke,

On Apr 16, 2014, at 9:29 PM, Luke Bloy wrote:

> Hi All,
> 
> I'm interested in using lcmv to do a common mode differential beamformer. My understanding, please correct me if I'm incorrect, is that the best way forward would be to
> 1) compute a covariance matrix from a time window combining both active and control windows.
> 2) use this combined covariance to make a common mode lcmv beamformer
> 3) apply this to both active and control windows separately
> 4) combine into some sort of psuedo T or NAI.
> 
> does this sound correct?

Yes it does.

> If so the main thing I'm unclear on is how to compute the covariance for 2 distinct time intervals? is this possible?

What you could do is call ft_timelockanalysis twice: each time with a different cfg.covariancewindow. Assuming you have an equal number of trials for both time windows, averaging the two covariance matrices will give you the combined covariance matrix.

Best,
Jan-Mathijs


> 
> Thanks,
> Luke
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Jan-Mathijs Schoffelen, MD PhD 

Donders Institute for Brain, Cognition and Behaviour, 
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands

Max Planck Institute for Psycholinguistics,
Nijmegen, The Netherlands

J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793

http://www.hettaligebrein.nl

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