[FieldTrip] Beamforming analysis in frequency band, concept problem

[smoratti at psi.ucm.es]

Hi Mikel,

I think Jörn gave you already the answer. You need enough time points to accurately estimate the oscillations of a frequency. For example in wavelet analysis (morlet) people use at least 5 cycles.

Best,

Stephan

________________________________________________________
Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Universidad Complutense de Madrid
Facultad de Psicología
Departamento de Psicología Básica I
Campus de Somosaguas
28223 Pozuelo de Alarcón (Madrid)
Spain

and

Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
Campus Montegancedo
28223 Pozuelo de Alarcón (Madrid)
Spain


email: smoratti at psi.ucm.es
Tel.:    +34 679219982

El 27/03/2012, a las 12:46, Ion Lavado escribió:

> Thank you Stephan, just one thing, why i need a time window big enough? so i'm just studying the frequency.
> 
> Best,
> 
> Mikel
> 
> 2012/3/27 Stephan Moratti <smoratti at psi.ucm.es>
> Dear Mikel,
> 
> I understand that you should do a mtmfft with a center frequency of interest (in your case cfg.foil = [11 11]) and then you do a frequency smoothing of 3 Hz (cfg.tapsmofrq = 3). Of course you need a time window big enough to allow such a smoothing. The CSD should represent a frequency window of 8 to 14 Hz then. Then you put the result of the mtmfft into the dics beamformer.
> 
> Best,
> 
> Stephan
>  
> El 27/03/2012, a las 11:19, Ion Lavado escribió:
> 
>> Hello, i'm having problems trying the beamformer analysis with a frequency band of interest. I would like to have for example an interval like [8 14] Hz. My concept problem is about the cfg.frequency and cfg.tapsmofrq  values. (it must be a escalar, but i want a frequency band). 
>> 
>> %FREQ ANALYSIS
>> cfg = [];
>> cfg.method    = 'mtmfft';
>> cfg.output    = 'powandcsd';
>> cfg.tapsmofrq = 5;
>> cfg.foilim    = [8 14];
>> freq_words_alpha = ft_freqanalysis(cfg, words);
>> 
>> 
>> %SOURCE ANALYSIS
>> cfg              = []; 
>> cfg.frequency    = 11;  
>> cfg.lambda=0;
>> cfg.method       = 'dics';
>> cfg.coordsys       = 'neuromag';
>> cfg.projectnoise = 'yes';
>> cfg.grad            =  freq_words_alpha.grad;
>> cfg.channel   = {'MEG'}; 
>> cfg.grid         = grid; 
>> cfg.reducerank      = 2;
>> cfg.vol          = vol02;
>> vol02=ft_convert_units(vol02,'cm');
>> source_pre11  = ft_sourceanalysis(cfg,  freq_words_alpha );
>> 
>> 
>> I use a cfg.frequency of 11 but i don't have really clear what i'm doing as a get the same result using cfg.frequency=11 but a freqanalysis in [10 12]. I would be very grateful if someone could solve my doubt.
>> 
>> Best wishes,
>> 
>> Mikel
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> 
> 
> ________________________________________________________
> Stephan Moratti, PhD
> 
> see also: http://web.me.com/smoratti/
> 
> Universidad Complutense de Madrid
> Facultad de Psicología
> Departamento de Psicología Básica I
> Campus de Somosaguas
> 28223 Pozuelo de Alarcón (Madrid)
> Spain
> 
> and
> 
> Center for Biomedical Technology
> Laboratory for Cognitive and Computational Neuroscience
> Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
> Campus Montegancedo
> 28223 Pozuelo de Alarcón (Madrid)
> Spain
> 
> 
> email: smoratti at psi.ucm.es
> Tel.:    +34 679219982
> 
> 
> 
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> 
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20120327/4933251a/attachment-0002.html>