[FieldTrip] freqanalysis
Victoria Schröder
victorias at dsv.su.se
Mon Feb 3 12:14:07 CET 2014
Thank Jörn,
Thank for the advice for the tutorials but i have already looked at
them a lot.
Anyhow, suppose i say cfg.keeptrials = 'yes', then i get the averaged
power over trials? what happens then when the trials do not have the
same length?
and a last question :)
what does cfg.toi depend on ? in the tutorial time frequency analysis
this is chosen : cfg.toi = -0.5:0.05:1.5; .. why is that the
case?
I hope this should be it for now
Best
Victoria
2014-02-03 11:42 skrev Jörn M. Horschig:
> Hi Victoria,
>
> you might want to read the relevant part of the walkthrough for your
> questions on mtmconvol and mtmfft:
> http://fieldtrip.fcdonders.nl/walkthrough#frequency_analysis
>
> Then, also doing this tutorial might help in understanding what the
> different methods are doing:
> http://fieldtrip.fcdonders.nl/tutorial/timefrequencyanalysis
>
> And lastly, to shortly answer your questions, see below ;)
>
> On 2/3/2014 11:15 AM, Victoria Schröder wrote:
>> Dear Jörn,
> Hi ;)
>
>>
>> the code works but i dont know whether my data is logical and
>> whether i decided to use the right method etc.
> maybe you should try to get into one of the FieldTrip courses :) This
> might tremendously help you in understanding what's being done and
> why. Otherwise, try to read as much as you can, read methods of
> papers
> and discuss with your supervisor and colleagues. Of course, on the
> mailing list we also like to help a lot.
>>
>> 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? yep, about right.
>
>> however, if i have more stimuli for one condition, how is the time
>> component then taken into account? it depends on how you segmented
>> your data. FieldTrip is just transforming your preprocessed data, so
>> whatever you put in is what you get out.
>
>> 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
>> seperatly?
> depends on whether you specify cfg.keeptrials = 'yes' or 'no'
>>
>> Say i would use cfg.method=mtmfft do i need to specify a
>> cfg.tapsmofrq when using cfg.taper='hanning'? no, a hanning taper is
>> always a single taper. Only when combining multiple tapers you can
>> effectively smooth in the frequency domain. this is implemented as
>> taper='dpss'
>
>> As i understand hanning if appropriate for lower freuquencies so i
>> should use this taper to assess beta frequencies.
> this is a rule of thumb, but there is nothing wrong with using
> multitapering for lower frequencies. It depends on what you expect
> from your data and what you want to achieve.
>>
>> Say i use cfg.method=mtmconvol what cfg.t_ftimwin is appropriate?
> this depends on the frequencies you are interested in. I wouldn't
> trust anything below 3 cycles, i.e. for 10Hz alpha at least 300ms.
>
>>
>> Thank you a lot for the help
> you're welcome, hope this helps
>> Best
>> Victoria
> Likewise,
> Jörn
>
>>
>>
>> 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
>>>> _______________________________________________
>>>> fieldtrip mailing list
>>>> 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:
>>> Trigon, room 2.30
>>> Kapittelweg 29
>>> NL-6525 EN Nijmegen
>>> The Netherlands
>>>
>>> _______________________________________________
>>> fieldtrip mailing list
>>> 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:
> Trigon, room 2.30
> Kapittelweg 29
> NL-6525 EN Nijmegen
> The Netherlands
>
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
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