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Message: 2<br>
Date: Fri, 16 Dec 2016 12:13:39 +0000<br>
From: "Bastiaansen, Marcel" <<a href="mailto:Bastiaansen4.M@nhtv.nl">Bastiaansen4.M@nhtv.nl</a>><br>
To: "'<a href="mailto:fieldtrip@science.ru.nl">fieldtrip@science.ru.nl</a>'" <<a href="mailto:fieldtrip@science.ru.nl">fieldtrip@science.ru.nl</a>><br>
Subject: [FieldTrip] phase distribution<br>
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Dear Fieldtrippers,<br>
<br>
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.<br>
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.<br>
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?).<br>
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...<br>
Can anyone give me advise on how to achieve my goal?<br>
<br>
Thanks,<br>
Marcel.<br>
<br>
<br>
***<br>
Dr Marcel C.M. Bastiaansen<br>
Lecturer and researcher in quantitative research methods<br>
Academy for Leisure & Academy for Tourism<br>
NHTV Breda University of Applied Sciences<br>
Visiting adress:<br>
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Email: <a href="mailto:bastiaansen4.m@nhtv.nl">bastiaansen4.m@nhtv.nl</a><mailto:<a href="mailto:bastiaansen4.m@nhtv.nl"><wbr>bastiaansen4.m@nhtv.nl</a>><br>
<br>
And<br>
<br>
Department of Cognitive Neuropsychology<br>
Tilburg School of Social and Behavioral Sciences<br>
Tilburg University<br>
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Email: <a href="mailto:M.C.M.Bastiaansen@uvt.nl">M.C.M.Bastiaansen@uvt.nl</a><<wbr>mailto:<a href="mailto:M.C.M.Bastiaansen@uvt.nl">M.C.M.Bastiaansen@uvt.<wbr>nl</a>><br>
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***<br>
</blockquote></div><br>hi Marcel,<br><br>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 <a href="http://www.fieldtriptoolbox.org/tutorial/timefrequencyanalysis">http://www.fieldtriptoolbox.org/tutorial/timefrequencyanalysis</a>) and by setting the parameter cfg.output = 'fourier' when you call the ft_freqanalysis function (see <a href="http://www.fieldtriptoolbox.org/reference/ft_freqanalysis">http://www.fieldtriptoolbox.org/reference/ft_freqanalysis</a>),<br><br>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,<br><br>Finalize for the statistical analysis, this can be done using non-parametric methods, and these functions are indeed implemented in Fieldtrip (see <a href="http://www.fieldtriptoolbox.org/tutorial/eventrelatedstatistics">http://www.fieldtriptoolbox.org/tutorial/eventrelatedstatistics</a>) so there must be a way to do this, otherwise you can implement your own permutation tests in Matlab,<br><br>The book (chapter 19 and 34) and web of Mike Cohen (<a href="http://mikexcohen.com/">http://mikexcohen.com/</a>) are excellent resources to implement all these calculations,<br><br>best,<br>Jose<br></div></div>