Questions on freqanalysis

[gao zai]

Dear Arjen,

Thanks for your great answer.
Have a nice day.

Best,
Feng

On Sun, Feb 14, 2010 at 7:16 PM, a.stolk at fcdonders.ru.nl <
a.stolk at fcdonders.ru.nl> wrote:

> Hi Feng,
>
> ft_freqanalysis; method mtmconvol can be considered as a frequency
> estimation shifting over time (in your case: -0.15 til 1.35 seconds). More
> specifically, every 0.05 seconds it makes an estimation of the
> powerspectrum. In order to so, one needs a certain timewindow to base the
> estimation on. The larger the timewindow, the better the estimation as one
> then averages over more cycles.
>
> You can either specify your timewindow with a steady length or let it be a
> function of the frequency. You chose the latter, which is fine. But when we
> consider timepoint "-0.15", frequency "5", and window "7 cycles"; the
> timewindow is 7 * 1/5 (5 hertz) = 1400 ms. At timepoint -0.15, this ranges
> from 700 ms before (-0.85 s) until 700 ms after. However, your data begins
> at -0.2 s and an estimation, therefore, can not be performed for this
> timepoint (-0.15 s) resulting in a NaN.
>
> You'll need to adjust one or more of the parameter settings (according to
> what is written above), or export more data from eeglab (with offsets), or
> live with the NaN's (they're displayed in white in ft_singleplotTFR). Also
> check out the TFR section in fieldtrip's tutorial section.
>
> Best,
>
> Arjen
>
> ----- Original Message -----
> From: "gao zai" <zaifengg at GMAIL.COM>
> To: FIELDTRIP at NIC.SURFNET.NL
> Sent: Sunday, February 14, 2010 11:16:31 AM GMT +01:00 Amsterdam / Berlin /
> Bern / Rome / Stockholm / Vienna
> Subject: [FIELDTRIP] Questions on freqanalysis
>
> Dear all,
>
> I am now trying to do the frequencyanalysis in Fieldtrip. Since the data is
> analyzed in EEGlab before, thus I first convert the data from EEGlab to
> Fieldtrip using eeglab2fieldtrip: *data = eeglab2fieldtrip(EEG,
> 'preprocessing' )*. The data was epoched from -200 ms to 1400ms time-locked
> to the onset of the stimuli.
>
> Then I run the following scripts:
>
> cfg              = [];
> cfg.output       = 'pow';
> cfg.method       = 'mtmconvol';
> cfg.taper        = 'hanning';
> cfg.foi          = 5:1:30;
> cfg.t_ftimwin    = 7./cfg.foi;  % 7 cycles per time window
> cfg.toi          = -0.15:0.05:1.35; % to reduce boundary effects
> TFRhann = freqanalysis(cfg, data);
>
> However, part of the result in TFRhann.*powspctrm* is *NaN*. And I didn't
> see any problem in the parameters I use. I wonder whether someone can give
> me some suggestions to fix it? Many thanks.
>
> Best,
> Feng
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the
> FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG
> and EEG analysis. See also
> http://listserv.surfnet.nl/archives/fieldtrip.html and
> http://www.ru.nl/neuroimaging/fieldtrip.
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the
> FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG
> and EEG analysis. See also
> http://listserv.surfnet.nl/archives/fieldtrip.html and
> http://www.ru.nl/neuroimaging/fieldtrip.
>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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