[FieldTrip] Number of epochs in the ft_freqanalysis output

[Federica Mauro]

Dear Stan and Elana, thank you very much for your answers and help.

Just another question: if I understood correctly, there's no way to compute
fft for single trials, since TFRhann.powspctrm is by definition an average
along trials. Is that true?

Thanks again.

Bests,
Federica

2015-12-14 13:21 GMT+01:00 Pelt, S. van (Stan) <stan.vanpelt at donders.ru.nl>:

> Dear Elana,
>
>
>
> The 50ms timesteps result in the 41 timebins. Per timebin, the average
> power spectrum (TFRhann.powspctrm) is computed over all trials that have
> data in that specific time bin. In your case, the power in the earlier time
> bins (e.g. 0.0s-0.05s) will be based on more data points (trials) than that
> of the later ones (e.g. 1.95-2.0s), because of your variable trial length.
>
>
>
> If you specify cfg.keeptrials=’yes’, you can see that the individual
> trial’s TFRs will have different amount of data points.
>
>
>
> Hope that helps.
>
>
>
> Best,
>
> Stan
>
>
>
> --
>
> Stan van Pelt, PhD
>
> Donders Institute for Brain, Cognition and Behaviour
>
> Radboud University
>
> Montessorilaan 3, B.01.34
>
> 6525 HR Nijmegen, the Netherlands
>
> tel: +31 24 3616288
>
>
>
>
>
> *From:* fieldtrip-bounces at science.ru.nl [mailto:
> fieldtrip-bounces at science.ru.nl] *On Behalf Of *Harris, Elana
> *Sent:* maandag 14 december 2015 13:12
> *To:* FieldTrip discussion list
> *Subject:* Re: [FieldTrip] Number of epochs in the ft_freqanalysis output
>
>
>
> cfg.toi          = -0:0.05:2;                  % time window "slides" from
> -0.5 to 1.5 sec in steps of 0.05 sec (50 ms)
>
>
>
> I just noticed this line has an error should be -0.5:0.5:2
>
>
>
> Sorry, I am new to fieldtrip myself and can't be more helpful yet.
>
>
>
> Cheers,
>
>
>
> Elana
> ------------------------------
>
> *From:* fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl]
> on behalf of Federica Mauro [federica.ma at gmail.com]
> *Sent:* Monday, December 14, 2015 6:30 AM
> *To:* FieldTrip discussion list
> *Subject:* [FieldTrip] Number of epochs in the ft_freqanalysis output
>
> Dear all,
>
>
>
> I'm having a problem in using the ft_freqanalysis function, so I'm writing
> to ask your help.
>
> I'm trying to get power data for each 2-seconds epochs of my eeg files.
>
> My eeg files are not of the same length (they don't have the same number
> of epochs), however the output of the function (namely TFRhann.powspctrm)
> always gives me power data for the same number of epochs, namely 41,
> unregarding of the effective number of epochs.
>
>
>
> Here is the code I'm using:
>
>
>
> cfg              = [];
>
> cfg.output       = 'pow';
>
> % cfg.channel
>
> cfg.method       = 'mtmconvol';
>
> cfg.taper        = 'hanning';
>
> cfg.foi          = 4:1:40;                         % analysis 2 to 30 Hz
> in steps of 2 Hz
>
> cfg.t_ftimwin    = ones(length(cfg.foi),1).*0.5;   % length of time window
> = 0.5 sec
>
> cfg.toi          = -0:0.05:2;                  % time window "slides" from
> -0.5 to 1.5 sec in steps of 0.05 sec (50 ms)
>
> TFRhann = ft_freqanalysis(cfg, eeg);
>
>
>
> Do you have any suggestion about it?
>
> Thank you very much for your attention.
>
>
>
> Worm regards,
>
> Federica
>
>
>
>
>
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