[FieldTrip] time frequency data looks blocky and stripy rather than smooth and swirly

[Stephen Whitmarsh]

Dear P.,

I suspect this is because:
1) you are using half a second for your sliding time-window, which is
reasonable, but only have 1.5 seconds of data, of which you plot only one.
This doesn't give much room for 'fuzzyness' in the sense of changes over
time.
2) because you are not baseline correcting the results, you will mosly see
1/f power, i.e. more power in the lower frequency bands, which will be
relatively stronger than any changes over time.

To solve this:
1) calculate the TFR over a longer time-window, both before and after
stimulation onset.
2) use a relative baseline correction

That should hopefully give you the fuzzyness you want.

Cheers,
Stephen

On Thu, 10 Jan 2019 at 06:14, Poppy Watson <popwatson at hotmail.com> wrote:

> Dear fieldtrippers,
>
>
>
> I’m replicating a study that used fieldtrip for TF analysis (and has some
> lovely single electrode TF plots  for each experimental condition). I’ve
> been running ft_freqanalysis using the following settings.
>
>
>
> cfg = [];
>
> cfg.trials  = trialsToUse; % this is a vector of trial numbers
>
> cfg.method = 'mtmconvol';
>
> cfg.output = 'pow';
>
> cfg.channel = 'eeg';
>
> cfg.taper = 'hanning';
>
> cfg.foi = 2:2:30;
>
> %cfg.t_ftimwin    = 4 ./ cfg.foi;
>
> cfg.t_ftimwin    = ones(length(cfg.foi),1).*0.5;
>
> cfg.toi = -1.25:0.10:0.25;   % 100 ms sliding time window
>
>
>
> The output and stats  etc seem to all make sense but my concern is that
> when I plot the data e.g. from one electrode (collapsed across the whole pp
> group)– I don’t get beautiful fuzzy TF graphs – instead I get very
> blocky/stripy figures like the attached where there doesn’t seem to be any
> smoothing/bleeding across different frequencies. I’ve tried playing around
> with the cfg.foi as well as the length of the time window and sliding
> window (cfg.t_ftimwin and cfg.toi) but the results always look very blocky
> rather than all warm and fuzzy (i.e. as seen in
> raw-TFdata-of-single-electrode images in various publications). Am I
> missing some smoothing parameters??
>
>
>
> This is my singleplot_TFR code:
>
>
>
> cfg = [ ] ;
>
> cfg.channel      = 'FCz';
>
> cfg.xlim         = [-1 0]; %before stimulus appears
>
> cfg.ylim         = [2 20]; % [8 12] only alpha
>
> cfg.zlim = [0 15];
>
> cfg.maskstyle    = 'saturation';
>
> cfg.masknans = 'yes';
>
> ft_singleplotTFR(cfg, allPPdata_suc_collapsed_high);
>
>
>
> Many Thanks
>
> P. Watson
>
>
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> https://doi.org/10.1371/journal.pcbi.1002202
>
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