# [Eeglablist] Question about EEG power

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Thu Nov 26 15:34:40 PST 2015

```Dear Carla and Ana,

I remember that when I tried to figure out the compatibility between Matlab
wavelet and EEGLAB newtimef(), it was confusing like hell.

Before converting to dB, EEGLAB newtimef() shows very large values (if you
intercept the process in the middle of code). But I'm not sure if it was as
big as 10^5 or 10^6. I understand that sounds intimidatingly large. At
least you have one paper that supports your observation/calculation, why
don't you publish the value?

For the spectrum density the unit is uV^2/Hz. EEGLAB uses it for spectrum
plot. Depending on definition of the measure you use a normalization factor
like that. Sorry I'm not very knowledgeable in these things either so may

Makoto

On Fri, Oct 23, 2015 at 7:29 AM, Carla Barros <carla.88.barros at gmail.com>
wrote:

> Dear all,
>
> We have been implementing a protocol for time-frequency analysis of EEG
> data using EEGlab, conducting a complex Morlet’s Wavelet analysis for
> spectral decomposition. The Morlet’s wavelet is defined using the MatLab
> function cmorwavf, and its parameters were set based on Roach and Mathalon,
> 2008 (length: 4-60Hz; step: 0.25Hz; number of cycles, temporal bandwidth,
> and bandwidth parameter (Fb) are computed according to the parameters c and
> m – c=7, m=4).
>
> We are interested in measuring PLF and total, evoked and induced power. We
> have computed the event-related power (across trials) by squaring the
> magnitude of the vectors obtained from the spectral decomposition, followed
> by baseline correction. The resulting power values were measured in μV^2,
> and their order of magnitude varies between 10^5 and 10^6. Based on the
> existing studies, it is difficult to get a sense of what should be the
> right range. For instance, Hamm et al., 2012 reported similar order of
> power magnitude, also measured in μV^2, using a similar time-frequency
> analysis method.
>
> Based on your experience, is this order of magnitude acceptable?
> Thank you very kindly in advance.
>
> Best regards,
> Carla Barros & Ana Pinheiro
>
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--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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