[FieldTrip] How this Warning: output time-bins artrial 30, frequency 4 (7.00 Hz) affect data? Differences in power spectrum and

[Helena Pereira]

Dear FieldTrip community,

I am a beginner using fieldtrip, so I know I am missing something in this
domain:
I am making a time-frequency analysis of EEG data with wavelets. However, I
am getting the following warning:

*Warning: output time-bins artrial 30, frequency 4 (7.00 Hz)*
*Warning: output time-bins are different from input time-bins*

Using this parameters:
    % Wavelet power
    cfg = []
    cfg.output = 'pow';
    cfg.channel = [1:64];
    cfg.keeptrials='no';
    cfg.method = 'wavelet';
    cfg.width = 7;
    cfg.toi = -2.0:0.01:2.0;
    cfg.foi = 4:1:20;

    p_stim = ft_freqanalysis(cfg,stim);

I can mitigate the warning by changing the cfg.toi from [ -2.0:0.01:2.0] to
  [ -2.0:0.5:2.0]

However, the plot of the spectrum changes a lot, as I expected as the time
window changes from intervals from 0.01 to 0.5:
With the warning:
[image: imagem.png]

Without the warning:

[image: imagem.png]


I know I am missing something regarding signal analysis... Why the
differences in the changing the step of the interval leads to the warning?

Can you help me? I am not sure if the warning can influence the final
results.

Best regards,
Helena Pereira
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