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

[Julian Keil]

Dear Poppy,

did you do some sort of baseline correction or condition contrast?
Otherwise, what you see is simply the 1/f distribution in the power spectrum.

Best,

Julian

________________
Prof. Dr. Julian Keil

Biological Psychology
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24118 Kiel, Germany

+49 - 0431 - 880 - 4872
http://www.biopsych.uni-kiel.de/en


> Am 10.01.2019 um 05:57 schrieb Poppy Watson <popwatson at hotmail.com>:
> 
> 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 <https://doi.org/10.1371/journal.pcbi.1002202>
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