[FieldTrip] phase synchronisation

["Jörn M. Horschig"]

Dear Hwee Ling,

this error most likely occurs because your data is rank-deficient. You 
can check this with the rank-function in Matlab.  However, when you are 
interested in phase synchronisation, there is no need to go down the 
path you are pursuing. You can just compute nonparametric measures, such 
as coherence, weighted phase lag index or the like. These work entirely 
on the cross-spectral density. Check out the help of 
ft_connectivityanalysis for more information.

Best,
Jörn

On 7/21/2014 3:11 PM, Hwee Ling Lee wrote:
> Dear all,
>
> I'm a bit confused with the computation of phase synchronisation.
>
> What I'm interested is to compute the phase synchronisation changes in 
> the second session (i.e. 1 year later) with respect to the first 
> session. There are 64 EEG channels in my data. I'm interested to 
> compute the mean phase coherence index.
>
> From the tutorial on 'analysis of sensor and source level 
> connectivity, it seems to me one has to first compute the multivariate 
> autoregressive model, follow by the spectral density function, follow 
> by non-parametric computation of the cross spectral density function 
> and finally the connectivity measures. However, when I tried to 
> compute the multivariate autoregressive model as suggested, I get an 
> error message:
>
> Error using chol
> Matrix must be positive definite.
>
> Error in armorf (line 40)
> ap(:,:,1) = inv((chol(ap(:,:,1)/Nr*(Nl-1)))');
>
> Error in ft_mvaranalysis (line 395)
>             [ar, tmpnoisecov] = armorf(dat, numel(rpt{rlop}), 
> size(tmpdata.trial{1},2), cfg.order);
> Can someone help me?
>
> Thanks!
>
> Cheers,
> Hweeling
>
>
>
>
>
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> fieldtrip at donders.ru.nl
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-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
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The Netherlands

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