[FieldTrip] phase distribution

[Jose]

> ------------------------------
>
> Message: 2
> Date: Fri, 16 Dec 2016 12:13:39 +0000
> From: "Bastiaansen, Marcel" <Bastiaansen4.M at nhtv.nl>
> To: "'fieldtrip at science.ru.nl'" <fieldtrip at science.ru.nl>
> Subject: [FieldTrip] phase distribution
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> Dear Fieldtrippers,
>
> I want to analyze data from an EEG experiment in which I split trials from
> one participant in two sets based on some response criterion.
> I want to know how (absolute) phase at a particular point in time (say
> t=0) is distributed within each set of trials, and whether there is (on
> average) a difference in absolute phase between the two sets of trials.
> I have found a matlab toolbox (circ_stats) that allows me to plot circular
> phase data, do tests on phase distributions, and to compare two
> distributions, but I would like to use Fieldtrip to extract the
> instantaneous phase angles (radians or degrees) from the single trials for
> a given point in time using multitapers (which I believe is the preferred
> method for this, right?).
> Browsing through the Fieldtrip discussion archive, I haven't been able to
> find a dedicated Fieldtrip function for that, but I am sure that functions
> such as  ft_mtmconvol do compute absolute phase at some point...
> Can anyone give me advise on how to achieve my goal?
>
> Thanks,
> Marcel.
>
>
> ***
> Dr Marcel C.M. Bastiaansen
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> And
>
> Department of Cognitive Neuropsychology
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> Tilburg University
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hi Marcel,

It seems you want to compute the clustering of phases across trials (a.k.a.
inter-trial phase clustering, ITPC). From what I've seen in Fieldtrip there
is no direct way to compute the ITPC, but it can be easily done with
abs(mean(exp(1i*phaseTimeSeries))) once you have the phase time series. You
can apply the function 'angle' to your analytic signal which is obtained
with any of the method that Fieldtrip has to decompose your signal (see
http://www.fieldtriptoolbox.org/tutorial/timefrequencyanalysis) and by
setting the parameter cfg.output = 'fourier' when you call the
ft_freqanalysis function (see
http://www.fieldtriptoolbox.org/reference/ft_freqanalysis),

>From what I know, please correct if I'm wrong, there is no preferred method
to do this. Multitaper is the preferred method to analyse fast oscillations
like gamma, but for ITPC any method that allow you to have phase time
series is enough,

Finalize for the statistical analysis, this can be done using
non-parametric methods, and these functions are indeed implemented in
Fieldtrip (see
http://www.fieldtriptoolbox.org/tutorial/eventrelatedstatistics) so there
must be a way to do this, otherwise you can implement your own permutation
tests in Matlab,

The book (chapter 19 and 34) and web of Mike Cohen (http://mikexcohen.com/)
are excellent resources to implement all these calculations,

best,
Jose
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