Wavelet vs. Multitaper

[Roni Tibon]

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?   

Thanks,
Roni  



----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: wavelet.jpg
Type: image/jpeg
Size: 93156 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20100503/1a5963a7/attachment.jpg>