[FieldTrip] Time frequency analysis using evoked potentials

[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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