[FieldTrip] Non linear frequency steps in TFR

[Lozano Soldevilla, D. (Diego)]

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 ----- Original Message -----
> From: " kousik sarathy " < sarathykousik @ gmail .com>
> To: " FieldTrip discussion list" < fieldtrip @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 @ 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
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> > fieldtrip @ 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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