Wavelet vs. Multitaper

Roni Tibon ronitibon at GMAIL.COM
Mon May 3 17:08:39 CEST 2010

Dear all,

I've been trying to analyze the same data using both methods, but I'm
getting very different results, depending on the method I'm using. 

Enclosed is a picture of the results of the analysis in 3 channels, using
both methods. In the left column I performed a multitaper analysis for each
channel, using the following script:

cfg = [];
cfg.output     = 'pow';
cfg.channel    = 'A195';
cfg.method     = 'mtmconvol';
cfg.foi        = 1:1:50;
cfg.t_ftimwin  = 2./cfg.foi;
cfg.tapsmofrq  = 0.4 *cfg.foi;
cfg.toi        = -0.2:0.05:1;
cfg.pad        = 'maxperlen';  
f12a_a195 = ft_freqanalysis(cfg, data);

In the right one, I performed wavelet analysis using:

cfg = [];
cfg.channel    = 'A195';
cfg.method     = 'wltconvol';
cfg.output     = 'pow';
cfg.foi        = 1:1:50;
cfg.width      =  1;
cfg.toi          = -0.2:0.05:1;
cfg.keeptrials = 'yes';
f12b_a195=freqanalysis(cfg, data); 

As you can see, channel A106 looks about the same using both methods.
However, for channels A176 and A195, the multitaper analysis revealed
activation in frequencies ranging from ~15-25, which was not seen in the
wavelet analysis. 

I used a different program (msi) to divide the trial in two (0-500ms and
500-1000ms) and compare activation in this frequency range between the 2
halves, and indeed- there was more activation in the second half, as would
be suggested by the multitaper. 

Can it be that when using wavelet analysis data is lost like this?
Am I doing something wrong with the wavelet?   


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