[FieldTrip] connectivity/amplitude correlation

[jan-mathijs schoffelen]

Dear Karl,

Perhaps I can add one or two things to Lilla's reply. If I understand your question correctly, it pertains specifically to the math behind the amplitude correlation computation, and how this is done in ft_connectivity_corr. It is indeed as you thought, the dimension over which the correlation is computed is indeed the trial dimension. That is, for each channelpair-time-frequency-point the amplitude correlation is computed across trials. A lot of the intelligence already takes place in ft_connectivityanalysis. In your case ft_connectivityanalysis computes the covariance (and variance) across trials between the amplitudes. The only thing that happens in ft_connectivity_corr is the normalisation with the square root of the variance product.

Hope this helps,

Jan-Mathijs

On Aug 27, 2012, at 4:16 PM, Karl Doron wrote:

> Hi Lilla,
> 
> There is a reference for Rosenberg et al, 1998 for the partialization method in the code itself but I'm not seeing any in the help section. 
> 
> Thanks,
> karl
> 
> 
> On Aug 27, 2012, at 2:59 AM, "Magyari, Lilla" <Lilla.Magyari at mpi.nl> wrote:
> 
>> Dear Karl,
>> 
>> There are four papers mentioned in the help of ft_connectivity_corr. I am wondering if any of those could answer your question.
>> 
>> Best,
>> Lilla
>> 
>> Karl Doron wrote:
>>> Hello,
>>> I'm wondering if there are any publications with the maths behind the functions for ft_connectivity_corr. I would specifically like to confirm (for a pending publication) how the amplitude correlation is computed when the function is given output from ft_freqanalysis which contains a time dimension (relevant cfg parameters pasted below). I've assumed this is occurring in the frequency domain across trials for sensor i and sensor j.
>>> cfg.channelcmb = chancmb;
>>> cfg.method     = 'mtmconvol';
>>> cfg.output     = 'fourier';
>>> cfg.keeptrials = 'yes';
>>> cfg.foi        = band(1):band(2);
>>> cfg.toi        = 1.8:0.01:3.0;
>>> Thanks for any feedback!
>>> Karl Doron, Ph.D.
>>> UC, Santa Barbara
>>> ------------------------------------------------------------------------
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>>> fieldtrip mailing list
>>> fieldtrip at donders.ru.nl
>>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
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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

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