[Eeglablist] EEG Alpha Asymmetry

[John J.B. Allen]

Dear Gregor

One thing to add:  typically you'd take the natural log of each site 
before subtraction.  And instead of left minus right, it's usually 
taken as right minus left. In Matlab, log takes the natural log.  So 
altering the code below, the asymmetry line would reflect these 
changes as follows:

asymmetry = log(spec_y(alpha_ind)) - Log(spec_x(alpha_ind))   % 
Asymmetry is the difference in the natural logs

Hope this is helpful

John

At 01:14 AM 8/8/2007, Arnaud Delorme wrote:
>Dear Gregor,
>
>first you need to compute alpha power. To do so may use the function
>spectopo or newtimef to compute the alpha power. For example for a
>single channel on the left and on the right.
>
>x = 10; % example of channel index on the left
>y = 11; % example of channel index on the right
>[ spec_x freqs ] = spectopo(EEG.data(x,:), EEG.pnts, EEG.frames, 'plot',
>'off');
>[ spec_y freqs ] = spectopo(EEG.data(y,:), EEG.pnts, EEG.frames, 'plot',
>'off');
>[tmp alpha_ind] = min( abs(freqs-10)); % find closest frequency to alpha
>at 10 Hz
>asymmetry = spec_x(alpha_ind) - spec_y(alpha_ind) % I think asymmetry is
>about subtracting power but I might be wrong.
>
>Hope this helps.
>Best regards,
>
>Arno
>
>gkohls at ukaachen.de wrote:
> > Dear all,
> >
> > I collected resting EEG to analyze frontal Alpha asymmetry. Can anyone
> > help me how to analyze alpha band and asymmetries with EEGlab? I tried
> > but did not succeed.
> >
> > Many thanks in advance,
> > Gregor
>
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