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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi Martin,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>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 Wavelets)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Best Ingrid<o:p></o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> <st1:PersonName
w:st="on">FieldTrip discussion list</st1:PersonName>
[mailto:FIELDTRIP@NIC.SURFNET.NL] <b><span style='font-weight:bold'>On Behalf
Of </span></b>Martin Bleichner<br>
<b><span style='font-weight:bold'>Sent:</span></b> Monday, December 01, 2008
2:48 PM<br>
<b><span style='font-weight:bold'>To:</span></b> FIELDTRIP@NIC.SURFNET.NL<br>
<b><span style='font-weight:bold'>Subject:</span></b> [FIELDTRIP] Different
results using multitapers and wavelet</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>hi there, <br>
<br>
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. <br>
<br>
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. <br>
In that case i get a kind of 'checkerboard' like time
frequency spectrum for the mutlitapers. <br>
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<br>
<br>
re there any prerequisites for multitaper use? Does anybody has some experience
with this effect? Do I do something wrong?<br>
Below you can find the cfg settings I am using<br>
<br>
Multitaper<br>
cfg.output ='pow'<br>
cfg.method='mtmconvol'<br>
cfg.tapers='dpss'<br>
cfg.toi=[-0.5:0.01:2.5]<br>
cfg.foi=[55:2:95]<br>
cfg.t_ftimwin=ones(size(cfg.foi))*0.2;<br>
cfg.tapsmofrq=ones(size(cfg.foi))*15; <br>
<br>
<br>
Wavelet<br>
cfg.method='wltconvol'; <br>
cfg.width=7;<br>
cfg.foi=[55:2:95]<br>
cfg.toi=[-0.5:0.01:2.5]<br>
<br>
Thanks<br>
<br>
Martin<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>----------------------------------<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>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.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>http://listserv.surfnet.nl/archives/fieldtrip.html<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>http://www.ru.nl/fcdonders/fieldtrip/<o:p></o:p></span></font></p>
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<p>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.</p>
<p> http://listserv.surfnet.nl/archives/fieldtrip.html</p>
<p> http://www.ru.nl/fcdonders/fieldtrip/</p>