[FieldTrip] computing threshold for PLV

smoratti at psi.ucm.es smoratti at psi.ucm.es
Sat May 18 20:11:11 CEST 2013

Dear Sheraz,

You might consult the following article: Lachaux, J. P. et al. 1999. Measuring Phase Synchrony in Brain Signal. Human Brain Mapping 8: 194-208. In principle you have to create surrogate data that represent the null hypothesis that there is no phase locking between your electrodes, sources, etc. Then you create hundreds or thousands of surrogate data sets and calculate each time you PLV. That way you create a distribution of your PLV values under the Null hypothesis. Then you check in what percentile your observed PLV lies (e. g. if its beyond the 95% percentile you would reject the Null hypothesis).

Hope that helps,


Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Universidad Complutense de Madrid
Facultad de Psicología
Departamento de Psicología Básica I
Campus de Somosaguas
28223 Pozuelo de Alarcón (Madrid)


Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
Campus Montegancedo
28223 Pozuelo de Alarcón (Madrid)

email: smoratti at psi.ucm.es
Tel.:    +34 679219982

El 18/05/2013, a las 18:21, Subramaniam Iyer escribió:

> Dear FT Experts,
> I have calculated PLV for a set of EEG data from 5 different patients. Now I want to convert the PLV matrix of each patient into a binary matrix. For this I need a threshold PLV value below which I can assume the phase locking is zero.
> My question is, how do I compute this threshold. I know hard thresholding is one option ( for ex setting 0.1 or 0.2 as threshold), but I guess it is not a very good option.
> Can somebody suggest a better and robust (statistical) way of determining the threshold ? 
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