[Eeglablist] Power Spectrum vs. Power Spectral Density

[Erickson]

Makoto and Ayda,

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.

Ayda, could you expand on what kind of normalization you mean?

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.

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.

Does anyone have a clearer perspective on this issue?

Brian


On Tue, Jun 3, 2014 at 5:08 PM, Ayda Ghahremani <ghahremani.aida at gmail.com>
wrote:

> Hi all,
>
> Regarding your question, I think power spectral density is normalized and
> is expressed in units per Hz. But, power spectra are not normalized.
>
> Ayda
>
>
> On Tue, Jun 3, 2014 at 3:28 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
>
>> Dear Brian,
>>
>> Actualy I did not know the difference. According to wikipedia, spectral
>> density is something like spectra represented as cumulative distribution
>> function.
>>
>> http://en.wikipedia.org/wiki/Spectral_density
>>
>> I don't know though when it is more appropriate to use power spectra and
>> spectral density... someone in the list please help us.
>>
>> Makoto
>>
>>
>> On Wed, May 28, 2014 at 8:50 AM, Erickson <ericksonb.eng at gmail.com>
>> wrote:
>>
>>> List,
>>> 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,
>>>
>>> - Brian
>>> Applied Brain and Cognitive Sciences Program
>>> Drexel University
>>>
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>>
>>
>>
>> --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
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