[FieldTrip] Best procedure for frontal alpha asymmetry

["Jörn M. Horschig"]

Dear Harsimrat,

I got some comments on your mail:

1. The alpha band is conventionally more around 10Hz, 14Hz is kind of 
the upper bound. 14-18Hz would be lower beta.
2. 2Hz resolution is fine.
3. All colleagues I know are running their frequency analysis on all 
channels, because there is no reason to separate channels in the 
analysis pipeline, neither methodologically nor for any other reason.
4. You might want to try to take the relative difference:

(tf.powspctrm (:,left,:,:) – tf.powsprctrm(:,right,:,:)) ./ (tf.powspctrm (:,left,:,:) + tf.powsprctrm(:,right,:,:))

or the like (e.g. log ratio), as this gives a normalized difference 
which makes comparisons across subjects somewhat easier. Also, it is 
more conventional, see e.g. Thut et al., 2006 for occipital alpha 
lateralization.

Good luck with your analysis!
Best,
Jörn

On 11/29/2012 2:38 PM, Harsimrat Singh wrote:
> Dear Fieldtrippers
>
> I am trying to calculate the difference in the alpha power on the
> frontal electrodes for a subject wise analysis.
>
> Can someone please suggest what will be the correct approach.
>
> Run freq analysis with alpha freq (14-18 ) with a resolution of 2Hz on
> all channels and then do
>
> tf.powspctrm (:,left,:,:) –tf.powsprctrm(:,right,:,:)
>
> OR
>
> run freq analysis on left chans and right chans separately and then do
> subtraction.
>
> Best regards
> Harsimrat
>
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-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

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