[FieldTrip] Using cfg.baseline and cfg.toi

[Eelke Spaak]

Hi Eno,

My hunch is that after the call to ft_freqanalysis, the time interval
comprising your baseline contains NaNs. The subsequent call to
ft_freqbaseline will subtract those NaNs from all time points, which
will result in all NaNs.

Have a look here to understand why there are NaNs after
ft_freqanalysis:
http://www.fieldtriptoolbox.org/faq/why_does_my_tfr_contain_nans And
then ensure you select a baseline window that does not contain NaNs.

Also, make sure to use *separate* cfg structs per FT function call to
avoid confusing yourself. So:

cfg = [];
...
freq = ft_freqanalysis(cfg, data);

cfg = [];
...
freq_bsl = ft_freqbaseline(cfg, freq);

Cheers,
Eelke

On 15 August 2018 at 22:32, Eno Umotong <enoumotong at hotmail.com> wrote:
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> Hi there,
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> I’m having trouble extracting the baseline from my time frequency data.
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> I’m using the function like this:
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> cfg = [];
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> cfg.output = ‘pow’;
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> cfg.channel = …
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> cfg.taper = ‘hanning’;
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> cfg.foi = …
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> cfg.t_ftimwin = ones(length(cfg.foi),1).*0.5;
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> cfg.toi = …
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> cfg.baseline = ..
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> cfg.baselinetype = ‘absolute’;
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> cfg.parameter = ‘powspctrm’;
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> freq = ft_freqanalysis(cfg, Dataset);
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> TFRHann3 = ft_freqbaseline(cfg,freq);
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> How can I use this function correctly please? I’m sorry to bother you with
> this. I couldn’t find assistance online. TFRHann3.powspctrum returns a
> matrix full of NaN. I’m sure this is obvious to you.
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> Just one more question. When selecting my time window of interest for
> frequency analysis using ft_freqanalysis and specifying cfg.toi, would 0
> represent my stimulus (as specified by epoch selection in eeglab interface)?
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> Many thanks again for your help.
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> Many thanks for your help.
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> https://doi.org/10.1371/journal.pcbi.1002202
>