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<div class="moz-cite-prefix">Hey Peter,<br>
<br>
when doing what Sheraz suggested you should, however, keep in mind
that the edges are computed using data outside your epoch, i.e.
possible muscle artifacts and other stuff (e.g. stimulation) will
corrupt the frequency estimation if not properly accounted for.
Make sure to note that when interpreting your data.<br>
<br>
Best,<br>
Jörn<br>
<br>
<br>
On 8/20/2012 5:18 AM, Peter Goodin wrote:<br>
</div>
<blockquote
cite="mid:A55BBE5A90EFC441A6FE147DF0DFE26EB58D1B@gsp-ex02.ds.swin.edu.au"
type="cite">
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charset=ISO-8859-1">
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<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">Thanks for that! Much appreciated.<br>
<div style="font-family: Times New Roman; color: #000000;
font-size: 16px">
<hr tabindex="-1">
<div id="divRpF638394" style="direction: ltr; "><font
color="#000000" face="Tahoma" size="2"><b>From:</b>
<a class="moz-txt-link-abbreviated" href="mailto:fieldtrip-bounces@science.ru.nl">fieldtrip-bounces@science.ru.nl</a>
[<a class="moz-txt-link-abbreviated" href="mailto:fieldtrip-bounces@science.ru.nl">fieldtrip-bounces@science.ru.nl</a>] on behalf of Sheraz Khan
[<a class="moz-txt-link-abbreviated" href="mailto:sherrykhan78@gmail.com">sherrykhan78@gmail.com</a>]<br>
<b>Sent:</b> Monday, 20 August 2012 11:29 AM<br>
<b>To:</b> FieldTrip discussion list<br>
<b>Subject:</b> Re: [FieldTrip] Wavelet advice<br>
</font><br>
</div>
<div>You can not avoid the border effects they comes from the
convolution.
<div><br>
</div>
<div>Only possible solution which I sometimes use when the
epochs are shorter due to the design, is to do the wavelet
decomposition on the continuous data, and then epoch it,
this will avoid the borders from the epoch.</div>
<div><br>
</div>
<div><span style="color:rgb(34,34,34);
font-family:arial,sans-serif;
font-size:12.727272033691406px;
background-color:rgb(255,255,255)">Sheraz</span><br
style="color:rgb(34,34,34);
font-family:arial,sans-serif;
font-size:12.727272033691406px;
background-color:rgb(255,255,255)">
<span style="color:rgb(34,34,34);
font-family:arial,sans-serif;
font-size:12.727272033691406px;
background-color:rgb(255,255,255)">Martinos Center</span><br
style="color:rgb(34,34,34);
font-family:arial,sans-serif;
font-size:12.727272033691406px;
background-color:rgb(255,255,255)">
<span style="color:rgb(34,34,34);
font-family:arial,sans-serif;
font-size:12.727272033691406px;
background-color:rgb(255,255,255)">MGH/MIT/Harvard</span>
</div>
<div><br>
<div class="gmail_quote">On Sun, Aug 19, 2012 at 7:20 PM,
Peter Goodin <span dir="ltr">
<<a moz-do-not-send="true"
href="mailto:pgoodin@swin.edu.au" target="_blank">pgoodin@swin.edu.au</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex; border-left:1px #ccc solid; padding-left:1ex">
<div>
<div style="direction:ltr; font-size:10pt;
font-family:Tahoma">Thanks for all the replies so
far.
<div><br>
</div>
<div>Re-reading my previous question I appear to
have been a bit vague to the overall problem. </div>
<div><br>
</div>
<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>
<div><br>
</div>
<div>What confuses me is that Kaplan et al, 2011 (<a
moz-do-not-send="true"
href="http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001267"
target="_blank">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>
<div><br>
</div>
<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>
<div><br>
</div>
<div>Peter<br>
<div>
<div style="font-size:16px; font-family:Times
New Roman">
<hr>
<div style="direction:ltr"><font
color="#000000" face="Tahoma"><b>From:</b>
<a moz-do-not-send="true"
href="mailto:fieldtrip-bounces@science.ru.nl"
target="_blank">
fieldtrip-bounces@science.ru.nl</a> [<a
moz-do-not-send="true"
href="mailto:fieldtrip-bounces@science.ru.nl"
target="_blank">fieldtrip-bounces@science.ru.nl</a>]
on behalf of Sheraz Khan [<a
moz-do-not-send="true"
href="mailto:sherrykhan78@gmail.com"
target="_blank">sherrykhan78@gmail.com</a>]<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>
</font><br>
</div>
<div>
<div class="h5">
<div>
<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>
</p>
<div class="gmail_quote">On Aug 19,
2012 7:17 AM, "Peter Goodin" <<a
moz-do-not-send="true"
href="mailto:pgoodin@swin.edu.au"
target="_blank">pgoodin@swin.edu.au</a>>
wrote:<br type="attribution">
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;
border-left:1px #ccc solid;
padding-left:1ex">
<div>
<div style="direction:ltr;
font-size:10pt;
font-family:Tahoma">Hi
Fieldtrip list,
<div><br>
</div>
<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>
<div><br>
</div>
<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>
<div><br>
</div>
<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>
<div><br>
</div>
<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>
<div><br>
</div>
<div>Advice on this subject
would be greatly
appreciated. </div>
<div><br>
</div>
<div>Peter.</div>
<div><br>
</div>
<div> </div>
</div>
</div>
<br>
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<pre wrap="">_______________________________________________
fieldtrip mailing list
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<br>
<pre class="moz-signature" cols="72">--
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands
Contact:
E-Mail: <a class="moz-txt-link-abbreviated" href="mailto:jm.horschig@donders.ru.nl">jm.horschig@donders.ru.nl</a>
Tel: +31-(0)24-36-68493
Web: <a class="moz-txt-link-freetext" href="http://www.ru.nl/donders">http://www.ru.nl/donders</a>
Visiting address:
Trigon, room 2.30
Kapittelweg 29
NL-6525 EN Nijmegen
The Netherlands</pre>
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