[FieldTrip] ft_freqanalysis wavelet problem

[Stephen Whitmarsh]

Dear Silvia,

The warning seems reasonable to me, as the output times probably don't map
perfectly on the input times. (BTW, your cfg.toi is rather dense, given
that you use a width of 7, you can probably increase the time intervals a
lot without losing much information, speeding it up as well)

Why you get a 'blue output' is hard to say, but you can set the zlim e.g.
as 'absmax'. Take a look at the ft_freqanalysis function help in the
beginning of the code (or type 'help ft_freqanalysis' in the MATLAB command
window), to see your options there. You might want to play with a baseline
correction in ft_freqanalysis to help visualise data with is otherwise
affected with 1/f power. Also, check out FieldTrip visualisation tutorial,
which should help you explore the options.

Best wishes,
Stephen

On 26 July 2018 at 09:57, Silvia Formica <Silvia.Formica at ugent.be> wrote:

> Dear all,
>
>
> I am new to fieldtrip so I apologize in advance if my question is trivial.
>
> I am trying to run a time frequency analysis with Morlet wavelets.
>
> Here is the code I am using:
>
>
> cfg = [];
> cfg.channel    = 1:64;
> cfg.method     = 'wavelet';
> cfg.pad        = 10;
> cfg.width      = 7;
> cfg.output     = 'pow';
> cfg.foi        = 4:1:30;
> cfg.toi        = 0:0.0039:2;    % my sampling rate is 512 Hz
> TFRwave        = ft_freqanalysis(cfg, data_clean);
>
>
> Where data_clean is the struct containing my trials. All my trials are
> the same length.
>
> When I run this code, I get the following warning:
>
> Warning: output time-bins are different from input time-bins
> trial 1, frequency 26 (29.00 Hz)
> Warning: output time-bins aretrial 2, frequency 25 (28.00 Hz)
> Warning: output time-bins aretrial 3, frequency 24 (27.00 Hz)
> Warning: output time-bins aretrial 4, frequency 25 (28.00 Hz)
> Warning: output time-bins aretrial 5, frequency 23 (26.00 Hz)
> [...]
>
> I have no idea what this means. Any suggestion?
>
> Despite the warning, the TRFwave is computed, but when I try to plot it I
> get a completely blue output. Here is the code I am using for the plot:
>
> cfg = [];
> cfg.baseline     = [-0.5 -0.1];
> cfg.baselinetype = 'absolute';
> cfg.zlim         = [-3e-27 3e-27];
> cfg.showlabels   = 'yes';
> cfg.layout       = 'biosemi64.lay';
> figure
> ft_multiplotTFR(cfg, TFRwave)
>
>
> When I check the content of my TFRwave I can see it is not made of NaNs.
> Is the problem due to the setting cfg.zlim? It is not clear to me how to
> set it.
>
> Thanks in advance for any help!
>
> Silvia
>
>
>
>
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> https://doi.org/10.1371/journal.pcbi.1002202
>
>
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