[FieldTrip] Time frequency analysis using evoked potentials

[Julian Keil]

Hi Alex,

just a very basic thought: Using a fixed zlim of [0 1] does not really make sense when using relative change (or absolute) baseline, as you could very well have values below zero post stimulus.
Also, when I compare your TFR Hanning (with absolute baseline) to the TFR Wavelet (with absolute baseline), they don't look too different, just badly scaled. Maybe you can play around with the zlim of the singleplot to get a better idea of what is happening here. Also, I wouldn't expect slightly different results from the wavelet vs. the mtmconvol as you are using different settings (e.g. 3 cycles width in the mtmconvol vs. 7 cycles in the wavelet).

Good luck,

Julian

Am 01.08.2017 um 11:52 schrieb Alexander Mentink:

> Hi Fieldtrip community,
> 
> I am trying to analyse time frequency representations of electrical evoked potentials, but I am not getting any reliable results at all.
> 
> Using hanning window (1-30 Hz) or (4-30 Hz), wavelet transform with absolute baselinetype and relative baselinetype gives me four totally different results (see link)
> 
> http://tinyurl.com/y7nerh8v
> 
> The EEG data is defined 1000 ms pre stimulus and 1200 ms post stimulus, artifacts removed and preprocessed with baseline correction between 200 ms and 0 ms, bandpass filtered between 0.5 - 30 Hz and referenced to earlobes. The timelocked analysis is attached to the dropbox link as well.
> 
> The code I use for hanning window is
> %%%%%%%%%%%%%%%%%%
> cfg = [];
> cfg.output       = 'pow';
> cfg.channel      = 'Cz';
> cfg.method       = 'mtmconvol';
> cfg.taper        = 'hanning';
> cfg.foi          = 1:0.025:30;  % OR 4:0.025:30
> cfg.t_ftimwin    = 3./cfg.foi;
> cfg.toi          = -0.5:0.01:0.7;
> TFRwave = ft_freqanalysis(cfg, trialdata);
> 
> % Visualization
> cfg = [];
> cfg.baseline     = [-0.5 -0.1];
> cfg.baselinetype = 'absolute';
> cfg.maskstyle = 'saturation';
> cfg.zlim         = [0 1];
> cfg.showlabels   = 'yes';
> figure
> ft_singleplotTFR(cfg, TFRwave)
> %%%%%%%%%%%%%%%%%%
> 
> And for wavelet transform is
> %%%%%%%%%%%%%%%%%%
> cfg = [];
> cfg.channel    = 'Cz';
> cfg.method     = 'wavelet';
> cfg.width      = 7;
> cfg.output     = 'pow';
> cfg.foi        = 1:0.5:30;
> cfg.toi        = -0.5:0.05:1;
> TFRwave = ft_freqanalysis(cfg, trialdata);
> 
> cfg              = [];
> cfg.baseline     = [-0.5 -0.1];
> cfg.baselinetype = 'relative'; % OR absolute
> cfg.maskstyle    = 'saturation';
> cfg.zlim         = [0 1];
> cfg.channel      = 'Cz';
> figure
> ft_singleplotTFR(cfg, TFRwave);
> %%%%%%%%%%%%%%%%%%
> 
> I have tried the tutorials online, but this doesn't give me any better results...
> 
> Does anyone know what I am doing wrong?
> 
> Thanks many times!
> 
> Best regards,
> 
> Alex (Master student
> 
> 
> 
> 
> Alexander Mentink
> Centre for Human Drug Research
> Zernikedreef 8
> 2333 CL Leiden
> The Netherlands
> T +31 (0) 71 7517166
> amentink at chdr.nl
> http://www.chdr.nl
> 
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