[Eeglablist] Electrodes Values

Arnaud Delorme arno at ucsd.edu
Sat May 18 10:21:40 PDT 2013


Dear Kleber,

one way to get a global measure proportional to microvolt is to use the Global Field Power (GFP).

http://sccn.ucsd.edu/pipermail/eeglablist/2008/002132.html

The root mean square (RMS) value is also sometimes used.
The root mean square value on average reference data is similar to the GFP (with small normalization difference).

tmp = rand(32,10); % simulated data 32 channels 10 points
std(tmp) % GFP
sqrt(mean(tmp.^2)) % RMS
sqrt(sum((tmp-repmat(mean(tmp), [size(tmp,1) 1])).^2)/(size(tmp,1)-1)) % RMS on average reference with n-1 normalization (same as GFP)

I am not sure RMS on a common reference should be used. Any other comments on this appreciated.
Thanks,

Arno

On 16 May 2013, at 15:15, Kleber de Aguiar wrote:

> Hello Everyone in this list,
> 
> I would like to know if anyone of you can answer me a doubt about de reading
> of the values of a group of electrodes in a EEG exam, as I"ll explain bellow:
> 
> 
> 1- Spliting the EEG recording in slots of time, that I will call them as
> "samples";
> 
> 2- Assuming that "n" electrodes were used in this EEG Recording;
> 
> 3 - In every "sample" of the recording, there will have "n" electrodes values
> corresponding for each electrodes;
> 
> MY QUESTIONS:
> 
> * How can I sum this electrodes values of the sample in a single value that
> represents  the total of microvolts oh that "sample"?
> 
> * How can I describe the values of "y" samples in a single value that
> represents these "y" sample values?
> 
> 
> Best regards,
> 
> Kleber, a fresh researcher in this field.
> 
> 
> 
> --
> Programa de Engenharia de Sistemas e Computação
> PESC/COPPE/UFRJ
> Visite nossa página web (http://www.cos.ufrj.br)
>        ------***------
> Kleber de Aguiar
> Tecnólogo em Sistemas de Computação
> Mestrando em Engenharia de Sistemas e Computação - PESC/COPPE/UFRJ
> Tutor Presencial CEDERJ/UAB - Curso de Computação UFF
> Twitter: @kleberIAguiar
> 
> 
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