query on coherence source analysis

Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Tue May 23 12:33:24 CEST 2006

Dear Muthuraman

At the Donders we usually use the multitaper method for computing the
cross spectral density, in freqanalysis that is cfg.method='mtmfft'
or 'mtmconvol'. If you would use the mtmconvol method, you will get a
frequency decomposition for multiple sliding time windows (that can
be overlapping or not). If you then would average these frequency
decompositions over time, you have performed Welch's method. We
already implemented that in a function, see attached
freqanalysis_mtmwelch (i.e. it even allows you to combine
multitapering and Welch). Add it to your fieldtrip directory and
specify cfg.method='mtmwelch' for freqanalysis.

This new function is still rather poorly documented, and it does not
have default settings for most of the cfg options. Probably you will
want cfg.taper=hanning (i.e. no multitapering), in which case you do
not have to specify cfg.tapsmofrq. The function will use maximally
overlapping windows for Welch method (which takes a lot of memory).
You should specify the frequencies of interest (cfg.foi) and window
length per frequency (cfg.t_ftimwin).


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On 22 May 2006, at 14:15, Muthuraman Muthuraman wrote:
> hello
> Thankyou for the previous suggestion
> I have gone through the article, in which for the 'DICS' algorthim
> it is mentioned that they use welch method to calculate the cross
> spectral density, for the freqanalysis program is there a
> cfg.method with welch to use it for the 'DICS'.
> I do not find the freqanalysis_mtmwelch
> I have the 20060131 version of fieltrip is it updated in the latest
> versions
> with regards
> muthu
>> From: Robert Oostenveld <r.oostenveld at FCDONDERS.RU.NL>
>> Reply-To: FieldTrip discussion list <FIELDTRIP at NIC.SURFNET.NL>
>> Subject: Re: [FIELDTRIP] query on coherence source analysis
>> Date: Tue, 2 May 2006 14:57:56 +0200
>> Dear Muthuraman
>> Fieldtrip implements DICS in the SOURCEANALYSIS function. You can
>> find the literature reference to the DICS algorith on the page
>> http:// www2.ru.nl/fcdonders/fieldtrip/doku.php?
>> id=fieldtrip:documentation:references_to_implemented_methods
>> best regards,
>> Robert
>> On 2 May 2006, at 11:02, Muthuraman Muthuraman wrote:
>>> Hello
>>> Thanks for the Previous suggestions
>>> i would like to know whether there is prescribed algorithm in
>>> Fieldtrip
>>> to calculate the coherent source analysis  between the EEG and
>>> EMG  data
>>> with regards
>>> muthuraman

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