# [FieldTrip] Intertrial coherence (phase locking factor)

jan-mathijs schoffelen jan.schoffelen at donders.ru.nl
Wed Mar 26 08:54:02 CET 2014

```Dear Beom Jun Min,

> I am confused with the 'cfg.method' for ITC.

There is currently no cfg.method that gives you ITC directly, indeed you should use the formula below, which is correct if you have a single taper per trial (which you have if you use cfg.taper = 'hanning' in ft_freqanalysis).

> After examining the previous discussion list, I found method for ITC calculation as below.
>
> tmpdat = freq.fourierspctrm;
> tmpdat = tmpdat./abs(tmpdat); % this will normalise each trial for its amplitude;
> itc = abs(mean(tmpdat)); % this will give the itc
>
> In addition, for this method, the ft_freqanalysis should have configuration as below.
>
> cfg = [];
> cfg.keeptrials = 'yes';
> cfg.keeptapers = 'yes';
> cfg.output     = 'fourier';
> cfg.channel    = 'all';
> cfg.method     = 'mtmfft';
> cfg.foi        = 20:1:60;
> cfg.toi = -0.5:0.01:1.5;
> cfg.tapsmofrq = 4;
> cfg.taper = 'hanning';
>
> However, I use 'wavelet' for the calculation of gamma band now.
>
> Should I use 'mtmfft' for the calucation of ITC?
>
> In case of 'wavelet', the result of itc has 4-D data - trial (averaged) * channel * freq * time
> Meanwhile, in case of 'mtmfft' the result has 3D data - trial (averaged) * channel * freq without time.
> Which structure is right?

The distinction between 'mtmfft' and 'wavelet'/'mtmconvol' is exactly whether time is taken into account. The functionality that you want to use, depends on your question.

> And, if I want to calculate the mean value of ITC of a group,
> is the order of the processing below right? :
> preprocessed data of each individual -> time-frequency analysis -> calculate ITC -> grandaverage

The order is correct.

Best wishes,
Jan-Mathijs

>
> With regards.
>
>
> --
> BeomJun Min, M.D.
>
> Department of Medical System Engineering (DMSE)
> Gwangju Institute of Science and Technology (GIST)
> 261 Cheomdan-gwagiro(Oryong-dong), Buk-gu, Gwangju
> 500-712, Republic of Korea (South)
> Phone: +82-62-715-3266 / Fax: +82-62-715-3244
> E-mail: mbj0310 at gmail.com, http://bmssa.gist.ac.kr
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

Jan-Mathijs Schoffelen, MD PhD

Donders Institute for Brain, Cognition and Behaviour,
Centre for Cognitive Neuroimaging,

Max Planck Institute for Psycholinguistics,
Nijmegen, The Netherlands

J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793

http://www.hettaligebrein.nl

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