[FieldTrip] plv and sourceanalysis

Stanley Klein sklein at berkeley.edu
Thu Apr 7 13:09:46 CEST 2011

Speaking of plv, two weeks ago I sent out a question regarding plv, but I
don't recall getting any responses. My questions were:

1) By ignoring the phasor magnitudes when summing over trials, isn't plv
noisier than standard coherence that includes magnitudes?

2) By including the real part isn't plv often dominated by volume conduction
that can be avoided by just looking at the imaginary part of coherence
(sadly the imaginary part may be hard to interpret and it ignores the
non-volume conducting contributions to the real part).

My original posting included:
*"I recall that when Lachaux et al. (1999) introduced it (I think it was
them) I didn't understand what is the advantage of adding unit magnitude
phasors. I would have thought that neglecting the magnitude of the phasor
would give a noisier measure of coherence.

Another worry is that the PLV includes the real part of the phasor which is
contaminated by the volume conduction from the forward model.  To avoid that
contamination many people only look at the imaginary part (the aspect of PLV
with 90 deg phase shift). The problem with the imaginary part is that one
loses the information from the non-volume conduction real part."*

thanks,  Stan

On Thu, Apr 7, 2011 at 3:55 AM, sibylle <s.mohr at psy.gla.ac.uk> wrote:

> Dear Fieldtrippers,
> I have a couple of question and I hope someone can help me:
> How is it possible to compute plv (for freq data)?
> As far as I can remember there used to be an option within
> ft_sourcedescriptives, which seems to have disappeared.
> How can one use plv to determine connectivity in source space?
> Thanks a lot & best wishes,
> Sibylle
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