# [FieldTrip] Questions about the phase estimation using multiple-tapper analysis.

Ruoyi Cao ruoyi.cao at mail.huji.ac.il
Mon Apr 5 17:23:54 CEST 2021

```Dear Community:
My name is Ruoyi.Cao and I am a PhD student in Leon Deouell lab in Hebrew
University of Jerusalem. I am currently working on Functional connectivity
data during working memory delay. In the experiment, I compared 2 PLV value
between two conditions.
The analysis followed the tutorial
https://www.fieldtriptoolbox.org/tutorial/connectivity/
For the functional connectivity, Instead of coherence, I computed the PLV
value.

Here is the step :
1: I first get fourier coefficient of the data by
cfg           = [];
cfg.method    =  'mtmfft';
cfg.taper     = 'dpss';%
cfg.output    = 'fourier';
cfg.tapsmofrq =3
cfg.foi          = 1:2:60
Tapper3freqB2{1}  = ft_freqanalysis(cfg, DataB2);

2:Then I put this output
cfg           = [];
cfg.method    = 'plv';
plvfreqB2 {P}          = ft_connectivityanalysis(cfg, Tapper3freqB2{1} );

Finally, I compared the plv value between conditions and found a robust
cluster through cluster-based permutation test.  However, I cannot
replicate the significant contrast between conditions if I used hanning
window with standard fft for calculating fourier coefficient.

I am writing to ask whether it makes sense to use all the output of
multi-tapper method, which is 3 times (taper number is 3) the original
trial number to compute the PLV value. What is the influence of the phase
estimation that muti-tapper analysis could cause. If the above procedure is
not wrong,  why the same results can not be replicated with hanning window
using one tapper.

Thank you so much
Best
Ruoyi
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