# [Eeglablist] Compute Amplitude Spectra in microvolts units using EEGlab

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Thu Feb 27 21:53:19 PST 2014

```Dear Joana,

...or apparently you can try the following...

% for your epoched data, channel 1
[spectra,freqs] = spectopo(EEG.data(2,:,:), 0, EEG.srate);

% delta=1-4, theta=4-8, alpha=8-13, beta=13-30, gamma=30-80
deltaIdx = find(freqs>1 & freqs<4);
thetaIdx = find(freqs>4 & freqs<8);
alphaIdx = find(freqs>8 & freqs<13);
betaIdx  = find(freqs>13 & freqs<30);
gammaIdx = find(freqs>30 & freqs<80);

% compute absolute power
deltaPower = 10^(mean(spectra(deltaIdx))/10);
thetaPower = 10^(mean(spectra(thetaIdx))/10);
alphaPower = 10^(mean(spectra(alphaIdx))/10);
betaPower  = 10^(mean(spectra(betaIdx))/10);
gammaPower = 10^(mean(spectra(gammaIdx))/10);

Makoto

2014-02-18 14:42 GMT-08:00 Makoto Miyakoshi <mmiyakoshi at ucsd.edu>:

> Dear Joana,
>
> Sorry for delayed response.
> I don't think spectopo supports it. However, if you use a debug mode or
> customize script to export the mid-products, you may get it.
>
> Makoto
>
>
> 2014-02-03 16:44 GMT-08:00 Joana Paiva <joanaispaiva at gmail.com>:
>
>> Hi,
>>
>> I would like to know how to compute amplitude spectra in microvolts units
>> instead microvolt^2/Hz units (PSD, output from spectopo) using EEGlab? I've
>> already tried using spetopo for spectral analysis but I couldn't convert
>> output values in microvolts units because I read that PSD consist in FFT
>> multiplied by the complex conjugate of the Fourier component.
>>
>> Thank you,
>> Best regards,
>>
>> --
>> *Joana Paiva*
>> MSc Student
>> Biomedical Engineering
>>
>> Faculty of Sciences and Technology - University of Coimbra
>>
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>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>

--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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