[Eeglablist] power spectrum versus power spectral density

[Agnieszka Zuberer]

Dear eeglab-community,

for our resting baseline measurements we would like to compute the power
for Theta, Alpha and Beta. In the eeglab-tutorial
<http://ch.mathworks.com/help/signal/examples/practical-introduction-to-frequency-domain-analysis.html>
we
read that calculating the power spectral density with pwelch would yield a
smoother power spectrum with power values closer to the expected values.

Our questions are:

   - What is the difference between power spectrum *(V^2/Hz)* and
   power-spectral density *(**watts/Hz)* in lay terminology for a
   non-electrophysiologist? Here we read tons of discussions on research gate
   and other pages, but the difference was mainly defined in units instead of
   really explaining the meaningful difference. Any literature on that would
   be highly appreciated.
   - what do we actually get out from averaging the power spectral density
   for a specific frequency range, coded as *mean(PSD(F>=fFreqency &
   F<=lastFreq))*; (e.g. fFreqency = 3.5 lastFrequency 7.5 for Theta)


Thank you very much in advance.
Agnieszka
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