<div dir="ltr">Hi,<br>Thanks for the quick response. <br>I tried using the settings you suggested, which, of course, reduced the frequency range, and revealed some activity in ~15-25hz, although it looked minor compared to that seen in the multitaper.<br>
<br>I guess my questions now are these:<br>1. How come when I use multitaper with 1 cycle I see a range starting at 5 hz, but when I use morelet wavelet with 1 cycle, the range starts at 10hz?<br>2. Can I conclude that when the trial is rather short multitaper will be more accurate, or more sensitive to changes?<br>
3. How come the freq range in the multitaper changes depending on the baseline settings? It started at 5hz when cfg.baseline = [-0.2 -0.05], but started at 10hz when cfg.baseline = [-0.2 -0.1];<br><br>Thanks a lot!<br>Roni <br>
<br> <br><br><div class="gmail_quote">On 3 May 2010 18:36, Roemer van der Meij <span dir="ltr"><<a href="mailto:r.vandermeij@donders.ru.nl">r.vandermeij@donders.ru.nl</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Roni,<br>
<br>
I haven't looked in detail at all the other settings you use, but you apparently use a different number of cycles for the wavelets in both methods. For the multitapers, you use 2 cycles per wavelet (which are then convolved with the set of dpss tapers), whereas you use 1 cycle for your Morlet wavelets (which are then convolved with a hanning taper (or something similar)). This will make the time-window for spectral estimation twice as long for the multitapers than for your Morlet wavelets. You could try setting cfg.width = 2 for 'wltconvol'.<br>
<br>
Hope it helps a bit,<br>
<br>
Roemer<div><div></div><div class="h5"><br>
<br>
<br>
<br>
On 5/3/2010 5:08 PM, Roni Tibon wrote:<br>
</div></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><div></div><div class="h5">
Dear all,<br>
<br>
I've been trying to analyze the same data using both methods, but I'm<br>
getting very different results, depending on the method I'm using.<br>
<br>
Enclosed is a picture of the results of the analysis in 3 channels, using<br>
both methods. In the left column I performed a multitaper analysis for each<br>
channel, using the following script:<br>
<br>
cfg = [];<br>
cfg.output = 'pow';<br>
cfg.channel = 'A195';<br>
cfg.method = 'mtmconvol';<br>
cfg.foi = 1:1:50;<br>
cfg.t_ftimwin = 2./cfg.foi;<br>
cfg.tapsmofrq = 0.4 *cfg.foi;<br>
cfg.toi = -0.2:0.05:1;<br>
cfg.pad = 'maxperlen';<br>
f12a_a195 = ft_freqanalysis(cfg, data);<br>
<br>
In the right one, I performed wavelet analysis using:<br>
<br>
cfg = [];<br>
cfg.channel = 'A195';<br>
cfg.method = 'wltconvol';<br>
cfg.output = 'pow';<br>
cfg.foi = 1:1:50;<br>
cfg.width = 1;<br>
cfg.toi = -0.2:0.05:1;<br>
cfg.keeptrials = 'yes';<br>
f12b_a195=freqanalysis(cfg, data);<br>
<br>
As you can see, channel A106 looks about the same using both methods.<br>
However, for channels A176 and A195, the multitaper analysis revealed<br>
activation in frequencies ranging from ~15-25, which was not seen in the<br>
wavelet analysis.<br>
<br>
I used a different program (msi) to divide the trial in two (0-500ms and<br>
500-1000ms) and compare activation in this frequency range between the 2<br>
halves, and indeed- there was more activation in the second half, as would<br>
be suggested by the multitaper.<br>
<br>
Can it be that when using wavelet analysis data is lost like this?<br>
Am I doing something wrong with the wavelet?<br>
<br>
Thanks,<br>
Roni<br>
<br>
<br>
<br></div></div>
----------------------------------<br>
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 <a href="http://listserv.surfnet.nl/archives/fieldtrip.html" target="_blank">http://listserv.surfnet.nl/archives/fieldtrip.html</a> and <a href="http://www.ru.nl/neuroimaging/fieldtrip" target="_blank">http://www.ru.nl/neuroimaging/fieldtrip</a>.<br>
<br>
</blockquote>
<br>
-- <br>
Roemer van der Meij MSc<br>
Scientific Programmer& Data-Analyst<br>
Donders Institute for Brain, Cognition and Behaviour<br>
Centre for Cognition<br>
P.O. Box 9104<br>
6500 HE Nijmegen<br>
The Netherlands<br>
Tel: +31(0)24 3612631<br>
E-mail: <a href="mailto:r.vandermeij@donders.ru.nl" target="_blank">r.vandermeij@donders.ru.nl</a><br>
<br>
----------------------------------<br>
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 <a href="http://listserv.surfnet.nl/archives/fieldtrip.html" target="_blank">http://listserv.surfnet.nl/archives/fieldtrip.html</a> and <a href="http://www.ru.nl/neuroimaging/fieldtrip" target="_blank">http://www.ru.nl/neuroimaging/fieldtrip</a>.<br>
</blockquote></div><br></div>
<p>----------------------------------</p>
<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>