[Mne_analysis] phase locking analysis with MNE

[Hari Bharadwaj]

Another reasonably easy route if you want to use all trials is to derive
the Null distribution non-parametrically by mixing all the 150 trials and
drawing many permutations of 50 and 100 trials respectively. There might
be some subtleties because variances are different for 50 and 100 trials
but its reasonable to ignore those higher order effects.

Regards,
Hari


On Thu, September 16, 2010 3:49 pm, Ghuman, Avniel (NIH/NIMH) [F] wrote:
> Yes, picking 50 randomly would be a good and easy remedy.
>
> I think the Raleigh distribution could also be used to "rescale" the PLV
> values, though I have to think about whether this would be valid from a
> statistical point of view (off the top of my head, you could transform
> your PLV values into probability values and compare the probability
> values, the problem is that I do not believe that probability values
> follow a normal distribution [particularly near 0 or 1], so there may be a
> further normalization step required).
>
>
> On 9/16/10 3:31 PM, "Matti Hamalainen" <msh at nmr.mgh.harvard.edu> wrote:
>
>
> On Sep 16, 2010, at 3:20 PM, Ghuman, Avniel (NIH/NIMH) [F] wrote:
>
> Hi All,
>
> PLV does in fact depend on the number of trials because it follows the
> Raleigh distribution.  Think of this like a chi-square distribution.  The
> mean/peak of the distribution will get closer to 0 as there are more
> trials, so your result is exactly what you would expect.  It does not have
> anything to do with the SNR however.
>
> For an example of this, calculate the PLV for random data with different
> numbers of trials.  You will see the PLV change.
>
> Hi all,
>
> So my guess was wrong. The obvious remedy then to pick N = 50 random
> trials from the N = 100 condition to make the two comparable, right?
>
> - Matti
>
>
> Avniel
>
>
> On 9/16/10 3:15 PM, "Matti Hamalainen" <msh at nmr.mgh.harvard.edu> wrote:
>
>
>
> On Sep 16, 2010, at 2:53 PM, Elisabeth Fonteneau wrote:
>
> Hi All,
>
> I am running a phase-locking analysis on MEG/EEG combined source
> data on the single trial level.
>
> And I have a quick question for this mailing list
>
> I was wondering whether the number of trials used for computing the
> Phase Lock Value (PLV) will affect the synchrony results?
>
> I meant if I am comparing 2 conditions with different numbers of
> trials in each (let's say N=50 vs N=100) do you think that the
> synchrony will change because of different signal to noise ratio?
>
> I am asking this because I have done such comparison, and strangely
> this is the condition with the less number of items that is showing
> increasing synchrony compared to the condition with the larger
> number (in the gamma band).
>
> It will be very helpful if somebody already came across this issue,
> and/or if you can point me toward a relevant paper discussing this
> problem.
>
> Thx to all for reading!
>
> To my understanding, the PLV should not depend on the number of
> trials. However, here are two tests you could do:
>
> 1. Pick N = 50 trials from the N = 100 condition a few times and check
> whether the PLV is the same as when using all the trials.
>
> 2. Using bootstrapping, you could calculate the variability
> (confidence intervals) of PLV in each condition to see whether this
> difference is true or just due to the variability in the data.
>
> - Matti
>
>
>
>
> ---------
>
> Matti Hamalainen, Ph.D.
> Athinoula A. Martinos Center for Biomedical Imaging
> Massachusetts General Hospital
>
> msh at nmr.mgh.harvard.edu
>
>
>
>
>
>
> _______________________________________________
> Mne_analysis mailing list
> Mne_analysis at nmr.mgh.harvard.edu
> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/mne_analysis
>
>
> The information in this e-mail is intended only for the person to whom it
> is
> addressed. If you believe this e-mail was sent to you in error and the
> e-mail
> contains patient information, please contact the Partners Compliance
> HelpLine at
> http://www.partners.org/complianceline . If the e-mail was sent to you in
> error
> but does not contain patient information, please contact the sender and
> properly
> dispose of the e-mail.
>
>
>
>
>
>
> ---------
>
> Matti Hamalainen, Ph.D.
> Athinoula A. Martinos Center for Biomedical Imaging
> Massachusetts General Hospital
>
> msh at nmr.mgh.harvard.edu
>
>
>
>
>
>
>
>
>
> _______________________________________________
> Mne_analysis mailing list
> Mne_analysis at nmr.mgh.harvard.edu
> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/mne_analysis
>
>
>


-- 
Hari Bharadwaj