<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="Section1"><p class="MsoNormal"><font size="2" face="Arial"><span style="font-size:10.0pt;
font-family:Arial">following the stimulus. However,
I noticed that during the course of the response, the dipole of the source
seemed to shift slightly, </span></font></p></div></div></blockquote><div><br></div><div>it really depends what you mean by "shift slightly". small shifts shouldn't be a big deal (i hesitate to give a rule of thumb). your dipole doesn't just capture activity from that one spot. of course if the movement is huge then placing a single dipole somewhere to represent that activity does not make sense.</div><br><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="Section1"><p class="MsoNormal"><font size="2" face="Arial"><span style="font-size:10.0pt;
font-family:Arial">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. </span></font></p></div></div></blockquote><div>the standard BESA approach e.g. would be to use a "regional source" i.e. a dipole with 3 orthogonal orientations. you can then calculate the vector magnitude (pythagoras). that should take care of a "rotating" dipole.</div><div><br></div><div>this can also be done within fieldtrip if you don't have BESA. </div><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="Section1"><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"><span class="Apple-style-span" style="font-family: Arial; font-size: 13px; ">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? </span></p></div></div></blockquote><div>pro:</div><div>- in case of "simple" activations (e.g. sensory evoked ERPs) you can reduce the information from >100 sensors to e.g. 2 sources. the dipole positions could also be standardized across subjects which may increase your power later when doing statistics (sensor positions are impossible to standardize without using offline tricks)</div><div>- of course neighbouring sources capture almost identical activity (which is good regarding you issue of "slightly shifting" source; see above), however the mixing of diverse activities is far worse on a sensor level!</div><div><br></div><div>cons:</div><div>- some arbitrariness of placing sources in "cognitive" experiments. unless you have very good prior information where to expect activity to come from, doing sensor analysis first followed by some distributed sources solution seems more advisable. you could then still look at time courses of ROIs defined by your statistical contrast.</div><div><br></div><div>in the end, there is no general cookbook-recipe and you should decide based on your experiment. the best situation is when your sensor and source data give converging results :-)</div><div><br></div><div>best,</div><div>nathan</div><div><br></div><br><blockquote type="cite"><div lang="EN-US" link="blue" vlink="purple"><div class="Section1"><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> <a href="http://listserv.surfnet.nl/archives/fieldtrip.html">http://listserv.surfnet.nl/archives/fieldtrip.html</a></p><p> <a href="http://www.ru.nl/fcdonders/fieldtrip/">http://www.ru.nl/fcdonders/fieldtrip/</a></p>
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<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>