[FieldTrip] FFT on a single concatenate trial

[elisa filevich]

Dear all, 

I'm doing frequency tagging on relatively short epochs. My frequency components are clearly there, but the signal-to-noise ratio is very low. In order to improve SNR, I want to try to concatenate the individual trials (with the appropriate epoch length to keep the frequency constant).

I simply concatenated all trial and timepoints vectors into a single trial structure, and I now have may data in a structure that has the following fields:
     

appended = 

      label: {1x22 cell}
    fsample: 512
       elec: [1x1 struct]
      trial: [22x157990 single]
       time: [1x157990 double]


I then run the FFT below, and I get the following error:

   error('the data does not contain a dimord, but it also does not resemble raw or component data');

Is it possible to run FFT on a single trial? Is there a way to work around this?

Best
Elisa


cfg              = [];
cfg.output       = 'pow';
cfg.channel      = 'all';
cfg.method       = 'mtmfft';
cfg.taper        = 'hanning';
cfg.foi          = 5:.5:35;
cfg.keeptrials   = 'no';
FFThann          = ft_freqanalysis(cfg, epoched);


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