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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Thanks for all the replies so far.
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<div>Re-reading my previous question I appear to have been a bit vague to the overall problem. </div>
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<div>The problem is I've used wavelets widths starting from 1 and increased to the default 7, but only a value of 1 gives me any usable data around 4Hz. </div>
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<div>What confuses me is that Kaplan et al, 2011 (<a href="http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001267">http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001267</a>) were able to get theta band activity
using epochs of 1s (200ms pre 800ms post) without apparent boundary effects at a width of 5, but when I tried the same thing (including zero padding), the results were not usable. </div>
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<div>Again, any advice and explanations as to why 1. a value of 1 is not usable and 2. why I may be getting these boundary effects would be greatly appreciated. </div>
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<div>Peter<br>
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<div id="divRpF498027" style="direction: ltr; "><font face="Tahoma" size="2" color="#000000"><b>From:</b> fieldtrip-bounces@science.ru.nl [fieldtrip-bounces@science.ru.nl] on behalf of Sheraz Khan [sherrykhan78@gmail.com]<br>
<b>Sent:</b> Monday, 20 August 2012 6:58 AM<br>
<b>To:</b> FieldTrip discussion list<br>
<b>Subject:</b> Re: [FieldTrip] Wavelet advice<br>
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<p>Hi,<br>
You can always try variables number of cycles may be start with 3 and then go to 5.<br>
Sheraz<br>
Martinos Center<br>
MGH/MIT/Harvard<br>
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<div class="gmail_quote">On Aug 19, 2012 7:17 AM, "Peter Goodin" <<a href="mailto:pgoodin@swin.edu.au" target="_blank">pgoodin@swin.edu.au</a>> wrote:<br type="attribution">
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<div style="direction:ltr; font-size:10pt; font-family:Tahoma">Hi Fieldtrip list,
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<div>I'm attempting to use wavelets to analyse some data collected with a neuromag system (sample rate of 500Hz, pre-trigger period is 200ms, post is 1.6 seconds) but am new to time frequency analysis. I'm interested in lower frequency bins (~4 to 20 Hz). The
config settings I've been playing with are as follows:</div>
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<div>cfg.method = 'wavelet';</div>
<div>cfg.channel = 'MEG';</div>
<div>cfg.keeptrials = 'yes';</div>
<div>cfg.foi = [4:1:20]</div>
<div>cfg.toi = [-.1:.01:1.5]</div>
<div>cfg.width = x </div>
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<div>Using a default width of 7, I'm getting large boundary effects leading to a period of ~300ms (400 - 700ms post trigger) of calculated data at 4Hz. I've played with the width and have found that a width of 1 gives only a small amount of boundary effect
at the extreme edges and shows a large increase in the frequencies I'm interested in at a time point which corresponds quite nicely with the ERF data also analysed. </div>
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<div>Having read the Tallon-Baudry (1999) article, material from the tutorials and items from the mailing list, I understand that by using a wavelet width of 1 I've biased my results towards higher temporal vs. spectral resolution, but considering the low range
of frequencies I'm interest in, is this a problem? Does using a low width with my cfg.foi set as it is just lead to a large amount of redundant data? </div>
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<div>Advice on this subject would be greatly appreciated. </div>
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<div>Peter.</div>
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