[Eeglablist] A question on ERS / ERD

[Joaquin Rapela]

Dear Marco,

By default EEGLAB computes ERSPs normalized to the baseline period. That is,

ERSP=10*log10(A/R)

Then, to compute ERS/ERD according to Pfurtscheller you should take:

(10.^(ERSP/10)-1)*100

where ERSP is the first output returned by the function timef in eeglab.

To see why this holds consider, from the above, that A/R=10^.(ERSP/10) then

(A-R)/R * 100 = (A/R-1) * 100 = (10^.(ERSP/10)-1)*100

Please reply back if anything is not clear.

Cordially, Joaquin

On Thu, Mar 15, 2012 at 02:48:43PM +0100, Marco Montalto wrote:
> Dear List,
> 
> Does anyone know whether the power values obtained in EEGLAB that by default are scaled to log(dB) i.e. (10*log(microvolt^2)), are usable for computing ERS / ERD using the method of Pfurtscheller, which is: (A - R) / R X 100 (where A is the power in the frequency band of interest in the period after the event and R is the power in the preceding baseline or reference period)?
> 
> Thanks and regards,
> Marco
> 
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-- 
Joaquin Rapela, PhD
Swartz Center for Computational Neuroscience
University of California San Diego
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San Diego, CA 92093-0559
tel: (858) 822-7536
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http://sccn.ucsd.edu/~rapela
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