Coherent sources

[R. Sreenivasan]

Hi Robert,

I find it difficult to figure out the hidden option of the frequency in
timelockanalysis. Would you please send me a sample script?

Thanks
Best regards, Sreenivasan

----- Original Message -----
From: "Robert Oostenveld" <roberto at SMI.AUC.DK>
To: <FIELDTRIP at NIC.SURFNET.NL>
Sent: Thursday, November 04, 2004 3:35 AM
Subject: Re: [FIELDTRIP] Coherent sources


> Hi,
>
> On 3 Nov 2004, at 15:48, R. Sreenivasan wrote:
>
> > Is it possible to compute coherence (sources)  for more than one
> > reference
> > dipoles (i.e, network) using Fieltrip?
>
> It is not possible to compute it with the frequency implementation of
> the beamformer (i.e. DICS). However, you could use the following
> approach
>
> - PREPROCESSING
> - TIMELOCKANALYSIS using a bandpass filter (which is a hidden option)
> in the frequency band of interest (not too narrow), with covariance=yes
> and keeptrials=yes
> - SOURCEANALYSIS with method=lcmv and singletrial=yes, with
> cfg.grid.pos equal to the locations of interest
> - FREQANALYSIS on the output of sourceanalysis, i.e. analyze the
> virtual channel that was constructed on each location of interest with
> output=powandcsd
> - FREQDESCRIPTIVES
>
> The sourceanalysis with method=lcmv and singletrial=yes will compute
> the average covariance matrix from your data and use that to construct
> the spatial filter. Subsequently the spatial filter is applied to each
> trial seperately. The reason for averaging the trials prior to applying
> the filters to the individual trials is that each individual trial
> covariance is probably rank deficient, and will at least be pooirly
> estimated resulting in poorly defined spatial filters. However, the
> spatial filter can be determined robustly from the average.
>
>
> best regards,
> Robert
>
> ----------------------------------------------------------------------
> Robert Oostenveld, PhD
> Center for Sensory-Motor Interaction (SMI)
> Aalborg University, Denmark
>
> and
>
> F.C. Donders Centre for Cognitive Neuroimaging
> University Nijmegen
> P.O. Box 9101
> NL-6500 AH Nijmegen
> The Netherlands
>
> Tel: +31 (0)24 3619695
> Fax: +31 (0)24 3610989
> ----------------------------------------------------------------------
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