<div dir="ltr">Makoto and Ayda,<div><br><div>Thanks for your responses. Yes, a PSD is expressed in units (power) per hz. A description I found in extensive online reading was "the PSD is the density of power at the specified Hz - therefore, in a suitably small window of Hz around the given point, the total power is equal to the width of the window multiplied by the PSD value." The PSD is a continuous function while the PS is a histogram.</div>
<div><br></div><div>Ayda, could you expand on what kind of normalization you mean?</div><div><br></div><div>The EEGLAB GUI option is "power spectra and maps." It's not clear that you're looking at a PSD unless you carefully inspect the units, which is potentially misleading. There were some other questions about it on this listserv, I think in 2012, and a bug report replied to by Arnaud, but it's not clear that this was ever addressed.</div>
<div><br></div><div>Personally my concern is in the implications of interpreting a PSD vs a PS. I have researched this question without much luck on Google. There is a lot of discussion but it is not conclusive. Some people report that interpretation is essentially identical, and others that there are important considerations to be made. However, most of the discussion focuses on electrical engineering principles that may not be relevant.</div>
<div><br></div><div>Does anyone have a clearer perspective on this issue?</div><div><br></div><div>Brian</div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Jun 3, 2014 at 5:08 PM, Ayda Ghahremani <span dir="ltr"><<a href="mailto:ghahremani.aida@gmail.com" target="_blank">ghahremani.aida@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi all, <div><br></div><div>Regarding your question, I think power spectral density is normalized and is expressed in units per Hz. But, power spectra are not normalized. </div>
<span class="HOEnZb"><font color="#888888"><div><br></div><div>Ayda</div>
</font></span></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Jun 3, 2014 at 3:28 PM, Makoto Miyakoshi <span dir="ltr"><<a href="mailto:mmiyakoshi@ucsd.edu" target="_blank">mmiyakoshi@ucsd.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Dear Brian,<div><br></div><div>Actualy I did not know the difference. According to wikipedia, spectral density is something like spectra represented as cumulative distribution function.</div>
<div><br></div><div>
<a href="http://en.wikipedia.org/wiki/Spectral_density" target="_blank">http://en.wikipedia.org/wiki/Spectral_density</a><br></div><div><br></div><div>I don't know though when it is more appropriate to use power spectra and spectral density... someone in the list please help us.</div>
<div><br></div><div>Makoto</div></div><div class="gmail_extra"><br><br><div class="gmail_quote"><div><div>On Wed, May 28, 2014 at 8:50 AM, Erickson <span dir="ltr"><<a href="mailto:ericksonb.eng@gmail.com" target="_blank">ericksonb.eng@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div dir="ltr">List,<div>The function "spectopo" produces output in units of 10log_10 (uV^2/Hz). This is power spectral density, as opposed to a power spectrum. Could anyone comment on the implications of interpreting, physiologically, the PS vs. the PSD of a neural signal? Thank you,</div>
<div><br></div><div>- Brian</div><div>Applied Brain and Cognitive Sciences Program</div><div>Drexel University</div></div>
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-- <br><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div>
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