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Hi Dorothy,<br>
<br>
This is a common problem (at least with auditory evoked potentials).
Some suggestions that worked for me in the past:<br>
<br>
1) use "initial seed points" that are approximately in the auditory
cortex (you can set the initial x,y,z points) before you do the
dipole fit<br>
2) make sure you have a good SNR (general comment for source
analysis, but seems to be extra important for DipFit)<br>
<br>
the reason that you're getting dipoles in the centre of the head is
that it "truely" is the best explanation of the variance, albeit it
doesn't make sense physiologically. <br>
<br>
cheers<br>
<br>
andrew<br>
<br>
<br>
On 12/30/2010 3:01 AM, Dorothy Bishop wrote:
<blockquote
cite="mid:01B4B1C924D5FC44B57B269548B562763C5909DF8D@EXMBX05.ad.oak.ox.ac.uk"
type="cite">
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<div dir="ltr"><font size="2" face="Tahoma"><font size="2"
face="Courier New"><font size="2" face="Courier New"><font
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<p>I am learning to use Dipfit2 with eeglab9_0_4_5s.</p>
<p><font face="courier new">All works well if I accept
default head model.</font></p>
<p><font face="courier new">I would like, however, to
modify the head model for children.</font></p>
<p> </p>
<p><font face="courier new">I followed the
instructions for doing this that I found in:</font></p>
<p><a moz-do-not-send="true"
href="http://sccn.ucsd.edu/pipermail/eeglablist/2007/001690.html"><font
color="#000000">http://sccn.ucsd.edu/pipermail/eeglablist/2007/001690.html</font></a></p>
<p> </p>
<p><font face="courier new">I kept everything the same
as for spherical 4 shell model, except that I
subsituted a new head model file with altered
vol.r values to correspond to 8 yr old child. I
also, on advice from a colleague, made</font></p>
<font size="2" face="Courier New"><font size="2"
face="Courier New">
<p>vol.c(3)=.0084</p>
<p> </p>
<p><font face="courier new">Output coordinates
default to MNI when you select custom model
file, and I kept this.</font></p>
<p> </p>
<p><font face="courier new">I then went to Edit
Channel locations to set head radius to be
same as last vol.r value, i.e. 70.3</font></p>
<p> </p>
<p><font face="courier new">I then ran autofit
dipoles , specifying 'fit bilateral dipoles'.</font></p>
<p><font face="courier new">But I end up with
single dipoles in the middle of the head.</font></p>
<p> </p>
<p><font face="courier new">I am not sure if the
problem is with my model specification, or
whether there is a bug, and would be grateful
for advice.</font></p>
<p> </p>
<p><font face="courier new">thanks</font></p>
<p> </p>
</font></font></font></font></font></font></div>
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<div class="BodyFragment"><font size="2">
<div class="PlainText">Dorothy Bishop, Professor of
Developmental Neuropsychology,<br>
Dept of Experimental Psychology, University of Oxford, OX1
3UD.<br>
tel +44 (0)1865 271369; fax +44 (0)1865 281255;<br>
WEB: <a class="moz-txt-link-freetext" href="http://www.psy.ox.ac.uk/oscci/">http://www.psy.ox.ac.uk/oscci/</a><br>
Blog: <a class="moz-txt-link-freetext" href="http://deevybee.blogspot.com/">http://deevybee.blogspot.com/</a></div>
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