[Mne_analysis] PLV in label in source space

[Laetitia Grabot]

Well, sure, I can share my code, but I'm using the deprecated function
induced_power... I didn't want to use the new tfr_morlet function because
it remains in sensor space.
Here is my script:
https://gist.github.com/anonymous/361c7ca1db3355c73618

Thanks Avniel for your precision! But do you think that it remains true
when you're using svd averaging? Moreover, I'm interested in an index
calculated as followed: [PLV(condition 1) -
PLV(condition1+2)]* [PLV(condition 2) - PLV(condition1+2)]. Thus this index
is proportional to PLV², and maybe it's why, when I compared the two index
pattern, I saw big differences  (I didn't try the stat yet).

Thanks again!
Laetitia

2014-09-19 17:58 GMT+02:00 Ghuman, Avniel <ghumana at upmc.edu>:

> Dear Alex and Laetitia,
>
> One thing to mention is that my experience is that the statistical
> significance does not change much either way. This has to do with the fact
> that averaging first boosts the SNR of the signal going into the PLV
> calculation, increasing the PLV values. If one calculates the PLV for each
> source, the individual PLV values are lower (lower SNR for each estimate),
> but because you have averaged many together, your confidence in the
> resulting PLV is increased. You can do this comparison using monte carlo
> or permutation testing, the p-values should not change much as long as you
> perform all of the same procedures on the permuted data as you did for the
> original data.
>
> Best wishes,
> Avniel
>
> On 9/19/14 11:50 AM, "Alexandre Gramfort"
> <alexandre.gramfort at telecom-paristech.fr> wrote:
>
> >hi,
> >
> >thanks for sharing these insights. Any suggestion to make this
> >straightforward
> >and update/deprecate source_induced_power is welcome.
> >
> >Laetitia if you can/want to share a gist it would be great.
> >
> >Alex
> >
> >
> >On Fri, Sep 19, 2014 at 4:54 PM, Ghuman, Avniel <ghumana at upmc.edu> wrote:
> >> Dear Laetitia,
> >>
> >> Generally I find that spatially averaging across the label, then
> >>calculating the PLV works better.
> >>
> >> Best wishes,
> >> Avniel
> >>
> >> From: Laetitia Grabot
> >><laetitia.grabot at gmail.com<mailto:laetitia.grabot at gmail.com>>
> >> Reply-To: Discussion and support forum for the users of MNE Software
> >><mne_analysis at nmr.mgh.harvard.edu<mailto:
> mne_analysis at nmr.mgh.harvard.edu
> >>>>
> >> Date: Friday, September 19, 2014 10:27 AM
> >> To:
> >>"mne_analysis at nmr.mgh.harvard.edu<mailto:
> mne_analysis at nmr.mgh.harvard.edu
> >>>"
> >>><mne_analysis at nmr.mgh.harvard.edu<mailto:
> mne_analysis at nmr.mgh.harvard.ed
> >>>u>>
> >> Subject: [Mne_analysis] PLV in label in source space
> >>
> >> Dear all,
> >>
> >> When calculating the phase-locking value (PLV) from n trials in a label
> >>in source space, I'm wondering if it is more relevant to:
> >> - spatially averaging the trials across the label, then calculated the
> >>PLV.
> >> - calculating the PLV on each source then averaging the PLVs across the
> >>label.
> >>
> >> I compared the two methods, and things change a lot (the PLV is larger
> >>when the average is done at the level of the trials than when it's done
> >>at the level of the PLVs). I would have the feeling that averaging the
> >>trials first is more relevant, especially if using svd, so that the
> >>averaged signal is more robust. Could someone confirm/contradict my
> >>feeling?
> >>
> >> Thanks in advance,
> >> Laetitia G.
> >>
> >>
> >>
> >>
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