query on coherence and layout

Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Mon Apr 3 22:22:02 CEST 2006

Hi Muthuraman

On 3 Apr 2006, at 11:00, Muthuraman Muthuraman wrote:
> I have used freqdescriptives to calculate the coherence between EEG
> and EMG
> the problem is i get a very less coherence value from 0.01 to 0.1
> is there the range specified in the programs

Coherence in the range from 0.01 to 0.1 in itself is not uncommon.
The values depend on the number of trials and tapers (since it is a
biassed measure). You should look at its spectral distribution and on
the scalp topography to see whether it makes sense.

> and what is the method you use to calculate the coherence can you
> give a brief explanation

Coherence is explained in books on signal processing, or you can do a
google for it. In Matlab you can also type "help CSD".

> i have also a problem with the layout
> i would like to create my own layout if it is  possible
> how it can be done
> because in the the previous mail you have mentioned about the
> elec1010 layout file
> but it does not match my requirements
> do i need the CTF software for this in all the layout files it is
> mentioned to be CTF 151 and so on.

You should open one of the layout files in a text editor as example.
The columns are
   number, xpos, ypos, width, height, label
You can manually make your own layout file in a text editor, or using
some custom matlab code if you already know within Matlab what your
electrode locations are.

best regards,

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