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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I want to calculate the strength of the evoked fields in
response to a series of stimuli. Initially, I tried doing this with the
averaged data at sensors demonstrating an evoked field following the stimulus. However,
I noticed that during the course of the response, the dipole of the source
seemed to shift slightly, and that this dipole was not consistently oriented
following successive stimuli. So I was concerned that by measuring only
the response at the sensor, I would obtain a false sense of change in the
underlying response. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> I decided to try looking at the response with the
data converted into the corresponding planar gradient (I use a CTF MEG). However,
I was unable to find a way to obtain values of the field within an ROI with
this data set. Does anyone know how to do this?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> Lastly, it seems it might be best to compute the source
and then evaluate the strength of the signal from an ROI in source-space. What
are the pros/cons of using sensor space vs. source space to measure the
amplitude of a response? Is there a convention within the field for the
methodology for doing this?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Beth Belluscio, MD-PhD<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Clinical Fellow<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Human Motor Control Section<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>National Institute of Neurological Disorders and Stroke<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>301-402-3495<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<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>