[FieldTrip] Imaginary part of coherence, 'indepsamplesZcoh'

Eric Maris e.maris at psych.ru.nl
Tue Apr 9 12:18:40 CEST 2013

Hi Ramin and Jörn,

In multiple-subject study, it is straightforward to statistically test
differences in imaginary coherence using Fieldtrip. This is analogous to
the statistical testing of regular coherence, which I outlined in a reply
to Ana.

For a single-subject study, you would have to write your own statfun. This
requires some skill, but it is conceptually straightforward. Importantly,
for any test statistic that you would like to use for comparing imaginary
coherence, you do not(!) have to know it’s parametric reference
distribution (thanks to the beauty of permutation inference (-;)


Eric Maris

From: "Jörn M. Horschig" [mailto:jm.horschig at donders.ru.nl]
Sent: vrijdag 5 april 2013 16:35
To: FieldTrip discussion list
Subject: Re: [FieldTrip] Imaginary part of coherence, 'indepsamplesZcoh'

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 :)


On 4/5/2013 9:49 AM, Ramin Azodi wrote:

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);
cfg.label     = freq.label;
stat = ft_freqstatistics(cfg, freq,freq1);

Thanks in advanced for your consideration.

Best Regards,

Ramin Azodi

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fieldtrip at donders.ru.nl

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
NL-6500 HB Nijmegen
The Netherlands

E-Mail: jm.horschig at donders.ru.nl
Tel:    +31-(0)24-36-68493
Web: http://www.ru.nl/donders

Visiting address:
Trigon, room 2.30
Kapittelweg 29
NL-6525 EN Nijmegen
The Netherlands
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