[FieldTrip] Non linear frequency steps in TFR

[Prasandhya Astagiri Yusuf]

Hi Kousik Sarathy and Diego,

thank you for your repply and suggestions!

Thanks a lot for the Field Trip links Diego, it helps me to understand how
Field Trip compute with wavelet. I thought field trip compute the wavelet
the same way as cwt function in Matlab (using scales instead of
frequencies).
Yes, I think I need to consider the frequencies "available" from my
computation and should be more aware of the spectral interpolation with
vulnerable spectral leakage.
I am still trying to play around with the parameters so I can get what I
want.

Cheers :)
Sandhy



On Fri, Aug 22, 2014 at 1:08 PM, Lozano Soldevilla, D. (Diego) <
d.lozanosoldevilla at fcdonders.ru.nl> wrote:

> Hi Sandhy,
>
> Could you please tell us a bit more info about how do you compute your
> TFR? Your problem sounds to me as your data length does not match the
> frequency you're asking:
>
>
> http://fieldtrip.fcdonders.nl/faq/why_does_my_output.freq_not_match_my_cfg.foi_when_using_wavelet_formerly_wltconvol_in_ft_freqanalyis
>
> http://fieldtrip.fcdonders.nl/faq/why_does_my_output.freq_not_match_my_cfg.foi_when_using_mtmconvol_in_ft_freqanalyis
>
> If you want to space frequency logarithmically, I'd recommend you to
> change the y-axes scale to log-scale after the TFR. Alternatively, other
> people approach the frequency resolution modifying the wavelets. You can
> make a modified wavelets with different number of cycles per frequency
> although this approach it's more vulnerable to spectral leakage. This is
> because the wavelet at particular frequency wont fit an interger number of
> cycles :
>
> cfg              = [];
> cfg.output       = 'pow';
> cfg.channel      = 'MEG';
> cfg.method       = 'mtmconvol';
> cfg.taper        = 'hanning';
> cfg.foi          = 2:1:50;
> cfg.t_ftimwin    = linspace(3,37.5,size(cfg.foi,2))./cfg.foi;
> cfg.toi          = -0.5:0.05:1.5;
> freq = ft_freqanalysis(cfg, data);
>
> I hope it helps,
>
> Diego
>
> ------------------------------
>
> *From: *"kousik sarathy" <sarathykousik at gmail.com>
> *To: *"FieldTrip discussion list" <fieldtrip at science.ru.nl>
> *Sent: *Friday, 22 August, 2014 11:13:22 AM
> *Subject: *Re: [FieldTrip] Non linear frequency steps in TFR
>
>
> Hey Sandhy,
>
> Try,
> cfg.foi = [7:30, 30:5:60, 60:10:120];
>
> Alpha and beta in steps of 1 Hz, low gamma in steps of 5 Hz and so on.
>
> Is this what you need?
>
>
> --
> Regards,
> Kousik Sarathy, S
>
>
>
> On Fri, Aug 22, 2014 at 11:01 AM, Prasandhya Astagiri Yusuf <
> prasandhya.a.yusuf at gmail.com> wrote:
>
>> Hi All,
>>
>> I want to have a TFR plot that has the same portion for :
>> - alpha (7-15 Hz)
>> - beta (15-30 Hz)
>> - low gamma (30-60 Hz)
>> - high gamma (60-120 Hz)
>>
>> Since those bands have exponential frequency steps, I could only see very
>> small part of alpha and (too) many  high gamma band. Is there a way to make
>> the cfg.foi in fieldtrip to have non linear steps? I tried to insert a
>> exponential function: cfg.foi = 0.5*exp(0.6931*(3.8:0.02:7.9));
>> But fieldtrip seems only detect first and last number and make linear
>> steps out of it.
>>
>> Thank you in advance for any help and share!
>>
>> Sandhy
>>
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>
>
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>
>
>
> --
> PhD Student
> Neuronal Oscillations Group
> Donders Institute for Brain, Cognition and Behaviour
> Centre for Cognitive Neuroimaging
> Radboud University Nijmegen
> NL-6525 EN Nijmegen
> The Netherlands
> http://www.ru.nl/people/donders/lozano-soldevilla-d/
>
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>
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