[Eeglablist] Spectopo function parameters

[Makoto Miyakoshi]

Dear Mohammed,

> What is the difference between these two mode?


This is from 'help std_spec()' which I entered as a blind guess :-)


    'specmode'   - ['psd'|'fft'|'pburg'|'pmtm'] method to compute spectral

                   decomposition. 'psd' uses the spectopo function (optional

                   parameters to this function may be given as input).
'fft'

                   uses a simple fft on each trial. For continuous data

                   data trials are extracted automatically (see 'epochlim'

                   and 'epochrecur' below). Two experimental modes are

                   'pmtm' and 'pbug' which use multitaper and the Burg

                   method to compute spectrum respectively. NOTE THAT SOME

                   OF THESE OPTIONS REQUIRE THE SIGNAL PROCESSING TOOLBOX.


> What is the method behind each of them?


Here is pwelch (i.e., 'psd')

https://en.wikipedia.org/wiki/Welch%27s_method


I guess the difference is that pwelch uses a sliding window with 50%
overlap and average, while fft uses a whole epoch to compute spectrum
density. If I'm wrong, someone please correct me!


> Is it possible to calculate logarithmic PSD using ‘psd’ mode?


Is it not already log-converted?


I know 'fft' results and 'psd' results look very different. Also, 'fft'
method provides less degrees of freedom in optional parameter input than
'psd'.


Makoto




On Fri, Sep 2, 2016 at 2:27 AM, Mohammed Jarjees <
m.jarjees.1 at research.gla.ac.uk> wrote:

> Dear all,
>
> I created study using EEGlab to compare the power spectrum density (PSD)
> between 4 groups for 2 conditions.
>
> I need to compute PSD using “Spectopo” . However, there are two option of
> the “Specmode” (‘fft’ and ‘psd’).
>
> I have try both of them and I got two different results.
>
>
>
> My questions are :
>
>                                      What is the difference between these
> two mode?
>
>                                      What is the method behind each of
> them?
>
>                                       Is it possible to calculate
> logarithmic PSD using ‘psd’ mode?
>
>
>
> Best Regrads
>
> Mohammed
>
>
>
>
>
>
>
>
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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