[Eeglablist] Coherence and Phase coherence

[arno]

Yossi Arzouan wrote:
> Hi
>  
>  
> 1. Is there any function in eeglab that calculate Phase coherence?
Yes, this is the crossf function that calculate (by default) the phase 
coherence between two variables.
>  2. Using crossf, to evaluate coherence between to signals (x1,x2 ) 
> that share one frequency (fr1) result in a coh value equally to 1 for 
> all frequencies ,  s! houldn't that result in coh = 1  only for fr1  ? 
If the coherence value is 1, it means that the two signal are identical. 
It then depends on how you constructed your signal. See below

a = rand(1,1000);
b = rand(1,1000);
afft = fft(a);
bfft = fft(b);
bfft(100:300) = afft(100:300); % afft contain a "miror power image" of 
itself (aff(2:500).^2 is the same as afft(end:-1:502).^2), so the code 
below is necessary
bfft(702:902) = afft(702:902);
aa = ifft(afft);
bb = ifft(bfft);
figure; crossf(aa,bb, 100, [-500 500], 100);

You will see a "band" of coherence = 1 at 20Hz

Best,

Arno
>  
> Yossi
>  
>
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