[FieldTrip] Negative values with debiased weighted phase lag index

Shephard, Elizabeth elizabeth.1.shephard at kcl.ac.uk
Fri Feb 17 12:41:09 CET 2017


Thanks Julian - I found the info I was looking for. Apologies - I should have checked the previous discussions first.


Best wishes

Lizzie

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Lizzie Shephard, PhD
Postdoctoral researcher
2.21 MRC SGDP Centre
Institute of Psychiatry, Psychology, & Neuroscience
King’s College London
De Crespigny Park
London, SE5 8AF
0207 848 5272
elizabeth.1.shephard at kcl.ac.uk



________________________________
From: fieldtrip-bounces at science.ru.nl <fieldtrip-bounces at science.ru.nl> on behalf of Julian Keil <julian.keil at gmail.com>
Sent: 17 February 2017 11:10
To: FieldTrip discussion list
Subject: Re: [FieldTrip] Negative values with debiased weighted phase lag index

Dear Lizzie,

this comes up from time to time on the Mailinglist.
Check for example this response by Martin Vinck:
https://mailman.science.ru.nl/pipermail/fieldtrip/2011-June/003892.html<https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmailman.science.ru.nl%2Fpipermail%2Ffieldtrip%2F2011-June%2F003892.html&data=01%7C01%7Celizabeth.1.shephard%40kcl.ac.uk%7Ccbe12a18f5fd4ba30c9c08d457264f41%7C8370cf1416f34c16b83c724071654356%7C0&sdata=uQ57ydU%2B3nFowiHUDFwvpV2usBijgVUOU8YPTJ%2FCkx8%3D&reserved=0>

Quote: The debiased WPLI estimator gets negative however as a consequence of the debiasing method - different issue.

Cheers,

Julian

Am 17.02.2017 um 12:05 schrieb Shephard, Elizabeth:

Dear all

I am using FieldTrip to explore connectivity in resting-state EEG data and aimed to use the debiased weighted phase lag index (dwPLI) to index this. However, I am finding a lot of negative values in my connectivity matrices when I compute the dwPLI, and I am unsure why this might be - has anyone found this previously, or have an idea of why this might be happening? I do not get this if I compute other connectivity measures (e.g. coherence) and I have a decent amount of clean trials (around 80 per subject) on which to run the connectivity. I am computing the dwPLI from fourier coefficients exported from a straightforward FFT.

Many thanks in advance for any advice
Best wishes
Lizzie

---------------------------------------------------------------------------
Lizzie Shephard, PhD
Postdoctoral researcher
2.21 MRC SGDP Centre
Institute of Psychiatry, Psychology, & Neuroscience
King’s College London
De Crespigny Park
London, SE5 8AF
0207 848 5272
elizabeth.1.shephard at kcl.ac.uk<mailto:elizabeth.1.shephard at kcl.ac.uk>


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