[FieldTrip] connectivity analysis with rereferenced EEG data

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Mon Jan 6 09:21:12 CET 2014

Hi Victoria,

exactly, since the rank of your matrix is reduced, you need to remove 
one channel from your data before computing the connectivity. I am not 
sure whether it is best to compute EEG-connectivity with 
average-referenced data or with a single channel reference. In case of a 
single-channel reference, you can of course remove the reference 
channel, so that'd be the easiest in that sense. Maybe check 
http://www.ncbi.nlm.nih.gov/pubmed/10619414 and related papers and 
decide for yourself how to reference ;)


On 1/3/2014 4:38 PM, Victoria Schröder wrote:
> Hello
> I am trying to do a connectivity analysis with Fieldtrip. I recorded 
> the EEG data with a BioSemi system without choosing a reference channel.
> Thus i need to select a reference in Fieldtrip. I did that during 
> ft_preprocessing(cfg) by using the following code:
> cfg.reref='yes';
> cfg.refchannel='all';
> Data=ft_preprocessing(cfg);
> however when i later want to do the ft_mvaranalysis(cfg, Data) i get 
> the following error:
> Matrix must be positive definite
> I read that this error probably occurs because the cfg.reref procedure 
> changes the ranks of the data matrix.However, i need to rereference my 
> data.
> Do somebody know a solution?
> All the best and thank you in advance
> Victoria
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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

E-Mail: jm.horschig at donders.ru.nl
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