[FieldTrip] a question regarding the code for PPC computation
Shen-Mou Hsu
explena at gmail.com
Fri Jul 7 05:21:58 CEST 2017
Dear FT users,
I am writing to request how pairwise phase consistency (PPC) is
implemented in Fieldtrip.
I trace the code and find that the following lines are relevant for PPC
computation
input = input./abs(input); % normalize the crosspectrum
outsum = nansum(input); % compute the sum; this is 1 x size(2:end)
c = (outsum.*conj(outsum) - n)./(n*(n-1)); % do the pairwise thing
in a handy way
However, when I try to verify the results by performing the equations
indicated by Vinck et. al. (2010), the outcomes are totally different from
those performed using ft_connectivity_ppc.
My code is as follows and many thanks for any help.
%%%%%%%%%%%%%%%%%%%%%%%%%
nTrial = size(input,1);
ppc_all = [];
for j = 1:(nTrial-1)
for k = (j+1):nTrial
ppc_temp = input(j,1,:,:).*conj(input(k,1,:,:));
ppc_all = [ppc_all;ppc_temp];
end
end
PPC = squeeze(abs(nansum(ppc_all,1)*2/(nTrial*(nTrial-1))));
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Best,
Shen-Mou Hsu
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