[Mne_analysis] phase locking analysis with MNE

[Matti Hamalainen]

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