[FieldTrip] Intertrial coherence (phase locking factor)
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.
> 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
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
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