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<p class="MsoNormal"><span style="color:#1F497D">Hi John, <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Using EEGLAB, the same head model is used for all of the individual subjects . So, I would assume you may have the same smearing problem in source localization as well. In addition, it is suggested that the
EEG head montage should be transformed to standard montage for all of the subjects ( after cleaning and channel rejection ) to provide the same montage for all of the subjects.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I like Scott explanation about my question. However, I am still thinking that it would be probably better if we first limit our time of interest ( for example to an ERP component like ‘P1’ ) and then apply the
source localization process on each individual subject. Using this method, we may get more relevant components which belong to same mental/cognitive/sensory/… process rather than clustering all of the components which are close to each other but not necessarily
involved in the same brain process. Any thoughts? <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="color:#1F497D">Best<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Iman <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="color:#1F497D"><o:p> </o:p></span></a></p>
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<p class="MsoNormal"><b>From:</b> RICHARDS, JOHN [mailto:RICHARDS@mailbox.sc.edu]
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<b>Sent:</b> Saturday, January 23, 2016 7:03 PM<br>
<b>To:</b> Iman Mohammad-Rezazadeh <irezazadeh@UCDAVIS.EDU>; EEGLAB List <eeglablist@sccn.ucsd.edu><br>
<b>Subject:</b> Re: [Eeglablist] EEG source localization in group level<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">An additional concern….<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">The EEG on the scalp is a result of a cortical source current and the composition of the individual participant head (skull, gm, wm, …). So when you average on the scalp, you are averaging data
across participants that was generated at a location in the participant head, but filtered by that participant’s head characteristics. The same “location” across individuals (e.g., an anatomical location) would come out with a different scalp distribution
across individuals because of differences in the head composition across individuals. I suspect this would lead to a smearing of the group average ERP and likely a different location when the source is analyzed on the grand average than when it is averaged
on the individual participants. Keeping the participant data intact (doing source analysis on the participant rather than the grand average) would remove this source of localization error.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">Ditto clustering of individual participants electrodes; electrode placement differs across individuals due to head size, different net placements, etc; and the relation of a nominally designated
electrode (#25; P3; P7) to the underlying cortical EEG generators differs across individuals given individual differences in head model composition across individuals.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">But is is common to assume that a single electrode nominally located across individuals is capturing signal from a common brain area, so we do grand average ERPs across individuals on a single
electrode, cluster ICA components across individuals based on electrode numbers, etc. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black">John<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">***********************************************<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">John E. Richards Carolina Distinguished Professor<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">Department of Psychology<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">University of South Carolina<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">Columbia, SC 29208<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">Dept Phone: 803 777 2079<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">Fax: 803 777 9558<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">Email: <a href="mailto:richards-john@sc.edu">richards-john@sc.edu</a><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">HTTP: jerlab.psych.sc.edu<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black">***********************************************<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:Consolas;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="color:black">From: </span></b><span style="color:black"><<a href="mailto:eeglablist-bounces@sccn.ucsd.edu">eeglablist-bounces@sccn.ucsd.edu</a>> on behalf of Iman Mohammad-Rezazadeh <<a href="mailto:irezazadeh@ucdavis.edu">irezazadeh@ucdavis.edu</a>><br>
<b>Date: </b>Tuesday, January 19, 2016 at 7:48 PM<br>
<b>To: </b>EEGLAB List <<a href="mailto:eeglablist@sccn.ucsd.edu">eeglablist@sccn.ucsd.edu</a>><br>
<b>Cc: </b>Scott Makeig <<a href="mailto:smakeig@ucsd.edu">smakeig@ucsd.edu</a>><br>
<b>Subject: </b>[Eeglablist] EEG source localization in group level</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:black">Hi EEGLABers, <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">I just wonder if anyone has done a research on the effect of averaging on source localization. In other words and in the group level analysis what is the difference between applying source localization on the grand
average data AND applying clustering method ( like EEGLAB) on sources based on individual subjects.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Thanks <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Iman <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="color:black">-------------------------------------------------------------</span></b><span style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="color:black">Iman M.Rezazadeh, Ph.D</span></b><span style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black">Semel Intitute, UCLA , Los Angeles<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"> <o:p></o:p></span></p>
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