[FieldTrip] freqanalysis

Victoria Schröder victorias at dsv.su.se
Mon Feb 3 11:15:07 CET 2014

Dear Jörn,

the code works but i dont know whether my data is logical and whether i 
decided to use the right method etc.

My trials are pretty long (approx 30 sec but all are not the same 
length) and i am interested in beta frequency.

First, it is not really clear to me whether i should use 
cfg.method=mtmfft or cfg.method=mtmconvol. As i understand ,  the latter 
calculates the FFT for shorter self-specified time windows to look at 
changes in power over time. Is that right? however, if i have more 
stimuli for one condition, how is the time component then taken into 
account? does mtmconvol take all trials of one condition and average the 
the power for each time window over all trials? Or is each trial treated 

Say i would use cfg.method=mtmfft do i need to specify a cfg.tapsmofrq 
when using cfg.taper='hanning'? As i understand hanning if appropriate 
for lower freuquencies so i should use this taper to assess beta 

Say i use cfg.method=mtmconvol what cfg.t_ftimwin is appropriate?

Thank you a lot for the help

2014-02-03 09:19 skrev Jörn M. Horschig:
> Hi Victoria,
> is there anything wrong with the code you used below? By smoothing,
> do you refer to smoothing in the frequency domain?
> Best,
> Jörn
> On 1/30/2014 11:33 AM, Victoria Schröder wrote:
>> Hello
>> I am currently working on a freqanalysis as a first step to do a 
>> connectivityanalysis. I am a bit unsure about the method to use for 
>> the freqanalysis. My stimuli are very long: between 29 and 30 sec. In 
>> total i have 4 stimuli per condition and 2 seperate conditions. I am 
>> looking at the beta range so fairly low frequencies.
>> this is my code:
>> Am i using the right taper and method. Should i smooth the data? and 
>> if so, what should such a smoothing parameter depend on?
>> %fourier analysis
>> cfg=[];
>> cfg.output='fourier';
>> cfg.method='mtmfft';
>> cfg.foi=[12:30];
>> cfg.taper='hanning';
>> cfg.keeptrials='yes';
>> cfg.channel={'C15' 'C10' 'B23' 'B3'};
>> frefourier=ft_freqanalysis(cfg,data_clean);
>> %coherence analysis
>> cfg=[];
>> cfg.method='coh';
>> cfg.channelcmb={'B3'  'C15'
>>                 'B3'  'C10'
>>                 'B23' 'C15'
>>                 'B23' 'C10'}
>> coherence=ft_connectivityanalysis(cfg, frefourier);
>> Thank you very much for the suggestions!
>> Best
>> Victoria
>> _______________________________________________
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>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> --
> Jörn M. Horschig
> PhD Student
> Donders Institute for Brain, Cognition and Behaviour
> Centre for Cognitive Neuroimaging
> Radboud University Nijmegen
> Neuronal Oscillations Group
> FieldTrip Development Team
> P.O. Box 9101
> NL-6500 HB Nijmegen
> The Netherlands
> Contact:
> E-Mail: jm.horschig at donders.ru.nl
> Tel:    +31-(0)24-36-68493
> Web: http://www.ru.nl/donders
> Visiting address:
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