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<div>I'm not sure about what you say because</div>
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<div><font size="2" face="tahoma">a) Relatively minor changes to the head model have led to single dipoles in middle of head rather than sensibly placed dipoles. The residual variance was below 2% per dipole with the adult head model and is now much higher.</font></div>
<div><font size="2" face="tahoma">b) I have explicitly asked for 2 dipoles per component, yet can only see one. I think I should be able to spot 2 superimposed dipoles in the output, even if the estimate is for a central location.</font></div>
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<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: http://www.psy.ox.ac.uk/oscci/<br>
Blog: http://deevybee.blogspot.com/</div>
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<font color="#000000" size="2" face="Tahoma"><b>From:</b> Andrew Dimitrijevic [adimitri@uci.edu]<br>
<b>Sent:</b> 31 December 2010 14:42<br>
<b>To:</b> eeglablist@sccn.ucsd.edu; Dorothy Bishop<br>
<b>Subject:</b> Re: [Eeglablist] modifying head model for children in dipfit2<br>
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<div>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>
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On 12/30/2010 3:01 AM, Dorothy Bishop wrote:
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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>
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<p><font face="courier new">I followed the instructions for doing this that I found in:</font></p>
<p><a href="http://sccn.ucsd.edu/pipermail/eeglablist/2007/001690.html" target="_blank"><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>
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<p>vol.c(3)=.0084</p>
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<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>
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<p><font face="courier new">thanks</font></p>
<p> </p>
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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/" target="_blank">
http://www.psy.ox.ac.uk/oscci/</a><br>
Blog: <a class="moz-txt-link-freetext" href="http://deevybee.blogspot.com/" target="_blank">
http://deevybee.blogspot.com/</a></div>
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