[Eeglablist] Power Analysis Units Question

[Lue, James C.]

Hi Folks,

I am a colleague of Sarah and wanted to add some context to her inquiry. We are conducting a time-series research design with single recordings, treating each recording as one epoch. We have event markers marking portions of the recording where the participant is performing the activity of interest. For each of these portions, our code is supposed to be calculating power spectral density for multiple frequency bands of interest.

For all our frequency bands, the values being returned to us are scaled from 0 to 1. They are clearly not in dB/Hz or uV^2/Hz. Output for this function was asked on MathWorks’ website.

https://urldefense.com/v3/__https://www.mathworks.com/matlabcentral/answers/32523-units-pmtm__;!!Mih3wA!HyUTQHUaMkKPhIM1d7AiYFPeCdWRayirpSMH_LOnitFsqiLCCgEOglTML9QP7SW6eG6vyBZR7Ju4f8LQr4cIdJ4GfNU$ 

The answer was the output from pmtm() is m^2/Hz. But what is m? We are hoping there is someone out there who is familiar with this function and knows its output. Alternatively, if there is another function that we should be calling instead to get dB/Hz or uV^2/Hz, that would also be helpful.

Regards,

James Lue
________________________________
From: eeglablist <eeglablist-bounces at sccn.ucsd.edu> on behalf of Newbolds, Sarah F. <sarah.newbolds at ou.edu>
Sent: Monday, March 20, 2023 2:05 PM
To: eeglablist at sccn.ucsd.edu <eeglablist at sccn.ucsd.edu>
Subject: [Eeglablist] Power Analysis Units Question

Hello,

We are using EEGlab to calculate a spectral power analysis using the following line of code:

[pxx(j,:,elecIdx), ~] = pmtm(x, [], freqBins, EEG.srate);

We wanted to see if anyone else is using this approach, as we are unsure of the units being reported for the power spectral density (the code was given to us). When plotted, the values are on a scale from 0-1, suggesting either a relative or normalized power spectral density, but the documentation for this function has been unclear as to the exact units of this output.

Thank you!

Sarah Newbolds
Ph.D. Student, Cellular & Behavioral Neurobiology Program, University of Oklahoma
Graduate Research Assistant, OU Visual Neuroscience Laboratory
B.A. Psychology, Benedictine College
785-991-1178

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