Different results using multitapers and wavelet
ingrid.nieuwenhuis at FCDONDERS.RU.NL
Mon Dec 1 15:51:00 CET 2008
If you use multitapers (or any frequency analysis) you have to take care
that you have an integer amount of cycles in your timewindow. Since you use
a fixed timewindow of 0.2 seconds, your frequency steps should be a multiple
of 5, so cfg.foi should be 55:5:95 or either you should use a cfg.timwin
which is dependent on the cfg.foi (fi 7 cycles, just as in your wavelets).
See the tutorial on the FieldTrip website for more explanation. (fieldtrip >
documentation > tutorial >Time-frequency Analysis Using Multitapers and
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Martin Bleichner
Sent: Monday, December 01, 2008 2:48 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] Different results using multitapers and wavelet
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
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
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
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.
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