[Eeglablist] Epochs - How to average epochs for power extraction

Clement Lee cll008 at eng.ucsd.edu
Tue Mar 23 10:36:49 PDT 2021

Hi Claudia,

You would be calculating spectopo (and then alphaPower) on EEG.data(2,:,:).
One way to check if you selected your events correctly by looking at the
size of EEG.data(2,:,:) and checking if the number of epochs and time
points are expected. You could also plot an epoch (e.g.
plot(EEG.data(2,:,1))) as a sanity check.

Clement Lee
Applications Programmer
Swartz Center for Computational Neuroscience
Institute for Neural Computation, UC San Diego

On Mon, Mar 22, 2021 at 6:30 PM Krogmeier, Claudia M via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Hi List,
> Thank you for any responses to the following question.
> I am hoping to use Makoto's code for extracting alpha power (found on
> wikipedia):
>  [spectra,freqs] = spectopo(EEG.data(2,:,:), 0, EEG.srate);  %channel 2
>  alphaIdx = find(freqs>8 & freqs<13);
>  alphaPower = mean(10.^(spectra(alphaIdx)/10));
> I have currently selected my event of interest (condition 3, for example),
> which contains several epochs.
> Can I assume that the alphaPower calculated will be from an average over
> the currently selected epochs?
> I am currently analyzing a single subject.
> Thank you!
> Claudia
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