[FieldTrip] ft_freqanalysis wavelet problem

Stephen Whitmarsh stephen.whitmarsh at gmail.com
Thu Jul 26 11:32:36 CEST 2018


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://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> https://doi.org/10.1371/journal.pcbi.1002202
>
>
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