Different results using multitapers and wavelet

[Martin Bleichner]

hi there,

I am using multitapers as well as wavelets to compute my time frequency
spectrum of ECoG data (50Hz-90Hz). Recently I realized some discrepancy
using these two methods, until than I found that these to method lead to
comparable results.

In one of our datasets we found very large differences between the two
methods. When I looked closer at the problem I found out that the two
methods lead to similar results when the effect (increase in power) is
large, while they deviate quite a bit when the effect is small.
In that case  i get  a kind of 'checkerboard'  like time frequency spectrum
for the mutlitapers.
I also compared the output of the frequency analysis with the bandpassed raw
signal and found that the wavelet transform was the better match. A

re there any prerequisites for multitaper use? Does anybody has some
experience with this effect? Do I do something wrong?
Below you can find the cfg settings I am using

Multitaper
cfg.output ='pow'
cfg.method='mtmconvol'
cfg.tapers='dpss'
cfg.toi=[-0.5:0.01:2.5]
cfg.foi=[55:2:95]
cfg.t_ftimwin=ones(size(cfg.foi))*0.2;
cfg.tapsmofrq=ones(size(cfg.foi))*15;


Wavelet
cfg.method='wltconvol';
cfg.width=7;
cfg.foi=[55:2:95]
cfg.toi=[-0.5:0.01:2.5]

Thanks

Martin

----------------------------------
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/fcdonders/fieldtrip.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20081201/8d440efa/attachment-0001.html>