[FieldTrip] suspiciously high plv

Akiko Ikkai akiko.ikkai at gmail.com
Thu Jun 28 20:30:50 CEST 2012

Dear FieldTrippers,

I've been trying to calculate chan-chan plv, based on the connectivity
tutorial (
http://fieldtrip.fcdonders.nl/tutorial/connectivity?s[]=connectivity) and
on past mailing-list posts. However, when I plot these plv, some plv are
really high, in .8-.9 range sometimes all the way into gamma range. It is
especially suspicious when channels that are in the opposite hemispheres,
separated in anterior-posterior axis show such high values. Does anyone
have any suggestions what might be going wrong? My script is pasted below.
I'm using Waveguard cap with 128 channels in Duke layout, sampled at 512
Hz, and average-referenced, and data are analyzed using fieldtrip-20120103

Thanks in advance, Akiko

 %%%% first define variables

chans = {'RD7','LL11','RA2','LC3'}; % let's try with these first...

testTime = [.8 2.5];


% choose time range

cfg = [];

cfg.toilim      = testTime; % extract delay period

ft_data         = ft_redefinetrial(cfg, ft_data);

% fourier transform

cfg           = [];

cfg.method    = 'mtmfft';

cfg.taper     = 'dpss';

cfg.output    = 'fourier';

cfg.keeptrials = 'yes';

cfg.keeptapers = 'yes';

cfg.tapsmofrq = 2;

cfg.channel   = chans;

freq          = ft_freqanalysis(cfg, ft_data);

% plv calc

cfg           = [];

cfg.method    = 'plv';

plv          = ft_connectivityanalysis(cfg, freq);

Akiko Ikkai, Ph.D.
Postdoctoral Fellow
Department of Psychological and Brain Sciences
Johns Hopkins University
Ames Hall, 3400 N. Charles St.
Baltimore, MD 21218
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