Hi Ingrid, <br><br>thanks for the tip, but it does not solve the problem. <br>I tried now the method that I am normally using for the low frequencies (hanning) for my high frequency range and get results comparable to the wavelet. See below. <br>
<br>Any other suggestions?<br><br>best<br>Martin<br><br><br><br>cfg.output ='pow'<br>
cfg.method='mtmconvol'<br>cfg.tapers='hanning'<br>cfg.toi=[-0.5:0.01:2.5]<br>cfg.foi=[55:2:95]<br>cfg.t_ftimwin=4./cfgLow.foi<br><br><br><div class="gmail_quote">2008/12/1 Ingrid Nieuwenhuis <span dir="ltr"><<a href="mailto:ingrid.nieuwenhuis@fcdonders.ru.nl">ingrid.nieuwenhuis@fcdonders.ru.nl</a>></span><br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Hi Martin,</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; 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)</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Best Ingrid</span></font></p>
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<p><b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;">From:</span></font></b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma;"> FieldTrip discussion list
[mailto:<a href="mailto:FIELDTRIP@NIC.SURFNET.NL" target="_blank">FIELDTRIP@NIC.SURFNET.NL</a>] <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> <a href="mailto:FIELDTRIP@NIC.SURFNET.NL" target="_blank">FIELDTRIP@NIC.SURFNET.NL</a><br>
<b><span style="font-weight: bold;">Subject:</span></b> [FIELDTRIP] Different
results using multitapers and wavelet</span></font></p>
</div><div><div></div><div class="Wj3C7c">
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">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</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>
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