[Eeglablist] A question on ERS / ERD

[Joaquin Rapela]

Dear Aleksandra,

To compute ERSPs in studies you should call the function std_ersp that accepts the optional parameters of the function newtimef. One of these optional parameters is called baseline that does what you want.

>From help std_ersp:

  Other optional inputs:
    This function will take any of the newtimef() optional inputs (for instance
    to compute log-space frequencies)...

>From help newtimef:

        'baseline'  = Spectral baseline end-time (in ms). NaN imply that no
                      baseline is used. A range [min max] may also be entered
                      You may also enter one row per region for baseline
                      e.g. [0 100; 300 400] considers the window 0 to 100 ms and
                      300 to 400 ms {default: 0 -> all negative time values}. 
                      This parameter is valid to define all baseline types below.
                      Once more "NaN" prevents baseline subtraction.

Please ask me more if anything is not clear.

Cordially, Joaquin

On Sun, Mar 18, 2012 at 10:45:15AM +0000, Aleksandra Vuckovic wrote:
> Dear Joaquin,
> do you know how to change the baseline period to calculate ERSP in a STUDY?
> Many thanks,
> Aleksandra
> 
> ________________________________________
> From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Joaquin Rapela [rapela at ucsd.edu]
> Sent: 18 March 2012 01:31
> To: Marco Montalto
> Cc: eeglablist at sccn.ucsd.edu
> Subject: Re: [Eeglablist] A question on ERS / ERD
> 
> 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
> 9500 Gilman Drive,
> San Diego, CA 92093-0559
> tel: (858) 822-7536
> fax: (858) 822-7556
> http://sccn.ucsd.edu/~rapela
> ----------------------------------
> 
> Yet who reads to bring an end however desirable? Are there not some pursuits
> that we practice because they are good in themselves, and some pleasures that
> are final? And is not this among them?  I have sometimes dreamt, at least, that
> when the Day of Judgment dawns and the great conquerors and lawyers and
> statesman come to receive their rewards--their crowns, their laurels, their
> names carved indelibly upon imperishable marble--the Almighty will turn to
> Peter and will say, not without a certain envy when He sees us coming with our
> books under our arms, ``Look, these need no reward. We have nothing to give
> them here. They have loved reading.''
>                                                            Orlando. A biography
>                                                            Virgina Woolf
> 
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-- 
Joaquin Rapela, PhD
Swartz Center for Computational Neuroscience
University of California San Diego
9500 Gilman Drive,
San Diego, CA 92093-0559
tel: (858) 822-7536
fax: (858) 822-7556
http://sccn.ucsd.edu/~rapela
----------------------------------

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tele, esa dichosa buena vida que nos gustaria pegarnos.

                                                   Fernando Savater
                                                   Ética para Amador

Percisely ethics aims at finding out what is about, beyond what we are told or
what we see on TV adds, that happy life that we aim at enjoying.

                                                   Fernando Savater
                                                   Ética para Amador