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Hi Brian, hi Makoto,<br>
<br>
as far as I know, and notwithstanding any considerations regarding a
particular software implementation, the PS yields the power of a
discrete, predefined set of frequencies interpretable as individual
values. In contrast, similar to the probability density of the
(standard) normal distribution, the PSD is a density function the
(partial) area under which can be interpreted in terms of power. The
transformation '10*log10' rescales to dB not affecting the units
(i.e. unit^2 and unit^2/Hz, respectively).<br>
<br>
Therefore, the choice between PS and PSD depends on the question you
want to answer. In EEG matters you are typically interested in the
power of continuous frequency bands and therefore should consider
the PSD (and determine the area within certain limits of interest).<br>
<br>
Ole<br>
<br>
<br>
<div class="moz-cite-prefix">Am 03.06.2014 23:26, schrieb
<a class="moz-txt-link-abbreviated" href="mailto:eeglablist-request@sccn.ucsd.edu">eeglablist-request@sccn.ucsd.edu</a>:<br>
</div>
<blockquote
cite="mid:mailman.132.1401830764.8038.eeglablist@sccn.ucsd.edu"
type="cite">
<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 moz-do-not-send="true"
href="http://en.wikipedia.org/wiki/Spectral_density">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">On Wed, May 28, 2014 at 8:50 AM,
Erickson <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:ericksonb.eng@gmail.com" target="_blank">ericksonb.eng@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">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>
<br>
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