# [FieldTrip] Imaginary part of coherence, 'indepsamplesZcoh'

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Fri Apr 5 16:34:33 CEST 2013

```Hi Ramin,

hope you are doing fine. For the imaginary part of coherence you need to
call ft_connectivityanalysis with cfg.output = 'imag'.
Afaik, z-scoring for the imaginary part is different from doing it for
the plain coherence, so you should not use indepsamplesZcoh. You could
have a look at Guido Nolte's paper on imaginary coherence and look it up
in the methods section how he is computing it - similar but different
from what I know how the z-scoring for coherence is computed. Thus, I am
not sure how to best do cluster-based statistics on that (that means, I
know how you could do it, but not what the best way to do it would be).
Of course, you write an own statistics function, something like
'indepsamplesZicoh'... but that would be tons of work.

Good luck! I hope anyone out there has other/better ideas :)

Best,
Jörn

On 4/5/2013 9:49 AM, Ramin Azodi wrote:
> Hello,
> In case that I want just to calculate imaginary part of coherence
> instead of coherence with 'indepsamplesZcoh', what kind of operation
> should I do for that? can anybody lead me through the right way ?
> You can find my code as following,
>
> cfg = [];
> cfg.method = 'mtmfft';
> cfg.output = 'fourier';
> cfg.taper  = 'hanning';
> cfg.foilim = [12 20];
> freq1 = ft_freqanalysis(cfg, data1);
> cfg = [];
> cfg.method = 'mtmfft';
> cfg.output = 'fourier';
> cfg.complex = 'imag';
> cfg.taper  = 'hanning';
> cfg.foilim = [12 20];
> freq2 = ft_freqanalysis(cfg, data2);
> cfg = [];
> cfg.method    = 'montecarlo';
> cfg.statistic = 'indepsamplesZcoh';
> cfg.parameter = 'fourierspctrm';
> cfg.computecritval = 'yes';
> cfg.numrandomization = 500;
> cfg.design = [ones(size(freq1.fourierspctrm,1),1);
> 2*ones(size(freq2.fourierspctrm,1),1)]';
> cfg.label     = freq.label;
> stat = ft_freqstatistics(cfg, freq,freq1);
>
> Best Regards,
> Ramin Azodi
>
>
>
>
>
>
>
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--
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Contact:
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