[Eeglablist] About ERSP averaging and normalisation

[Kazuhiro Shishida]

Dear Marco,

Marco Buiatti <marco.buiatti at univ-paris5.fr> wrote:

> 2) The non-linearity of the log causes averages over electrodes/subjects 
> to be biased: don't you think this can be misleading?

The average of logarithmic value is the radical of products, for example,
when A is a 1 x n vector,
mean((log10(A)),2)=log10(prod(A,2)^(1/n)).
Of course, it's different from log10(mean(A,2)).
So, it is a problem which is physiologically better. I think intuitively that the former one is better, but also eager to know the answer about it.

> 4) This is more a prayer than a question, since the question has been 
> asked several times: a tool to quantify the statistical difference 
> between two conditions would be highly appreciated!
> 
I also want to have these kind of tools. I think one solution is to compare the upper limit of bootstrapped data of one condition and lower limit of another condition. But this method does not preserve much data as having statistical significance, instead, much are killed. Other way is to compare RMS or peak magnitide of ERSP quantitatively. Does someone know other solution?

Best,

Kazuhiro Shishida

Department of Psychiatry and Neurosciences, Hiroshima University
1-2-3 Kasumi Minamiku, Hiroshima, Japan


> Little thing to correct: when using tftopo, 'mode','ave', the message 
> 'RMS averaging' is printed, while it seems to me that normal averaging 
> is performed.
> 
> Thank you,
> 
> Marco
> 
> -- 
> Marco Buiatti
> 
> Neurophysique et Physiologie du Systeme Moteur - CNRS UMR 8119
> UFR biomedicale Les Saints-Peres
> 45 rue des Saints-Peres 75270 Paris cedex 06
> Tel: +33(0)142862146
> Fax: +33(0)149279062
> http://www.neurophys.biomedicale.univ-paris5.fr/~buiatti/
> 
> 
> 
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