<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">hi jan-mathijs,<div><br></div><div>thanks once again for your quick help.</div><div><br></div><div>it's about 60 trials which was sufficient in the past. the decrease is bilateral, however i can't imagine how this could lead to a more or less pronounced increase after sourceanalysis. in case of a DICS problem wouldn't the decrease just be placed somewhere in between the two spots?</div><div><br></div><div>the labels in data.label, data.grad.label match. they also have the same order as in the .xyz file from the BTI system.</div><div><br></div><div>for the sourceanalysis we precompute the leadfield. as a side note we also use predefined grid points so that they are exactly the same within one subject across conditions.</div><div>one issue that we noticed is that we recalculated a leadfield that we calculated a long time ago and compared the values. they appear not to be exacly the same. when looking at the topographies (forward solution) yieldied by each source, they are similar but not exactly the same. is this possible?</div><div>I'm attaching a plot. for each dipole i calculated the vector sum over orientations and averaged the energy over sensors. this i did for the old and the newly calculated leadfield. in the plot difference between the two leadfields is shown on y and dipole number on x.</div><div><br></div><div>here's the code:</div><div><div>%% checke tzvetans grid mit neuer FT</div><div><br></div><div>cd /home/nadia/Matlab/zvetanskopf</div><div><br></div><div>tvol=load('vol'); %old vol</div><div>tgrid=load('grid'); %old grid</div><div><br></div><div>%%</div><div>cfg=[];</div><div>cfg.grid.pos=tgrid.grid.pos;</div><div>cfg.grid.dim=tgrid.grid.dim;</div><div>cfg.grid.inside=tgrid.grid.inside;</div><div>cfg.grid.outside=tgrid.grid.outside;</div><div>cfg.vol=tvol.vol;</div><div>cfg.grad=tgrid.grid.cfg.grad;</div><div>cfg.channel=tgrid.grid.cfg.channel;</div><div><br></div><div>tgrid.grid2=prepare_leadfield(cfg); %new grid</div><div><br></div><div>%%</div><div><br></div><div>for i=1:length(tgrid.grid2.inside)</div><div>diffLF(i)=mean(sqrt(sum(tgrid.grid.leadfield{tgrid.grid2.inside(i)}.^2,2)))-mean(sqrt(sum(tgrid.grid2.leadfield{tgrid.grid2.inside(i)}.^2,2)));</div><div>end</div><div><br></div><div>plot(diffLF)</div><div><br></div><div>thanks for any input.</div><div><br></div><div>nathan</div></div><div><div><div><br></div></div></div><div><br></div><div><br></div><div><img height="480" width="551" apple-width="yes" apple-height="yes" src="cid:AE425F5E-242D-4F61-83E4-FE51184F8F0C@zpr30.psychologie.uni-konstanz.de"><br><div><div>On 19.11.2008, at 14:13, jan-mathijs schoffelen wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "> Dear Nathan,<div><br></div><div>Are you using precomputed leadfields? The reason I ask is because there could be a discripancy between the assumed order of the coils in your leadfields, and the coil-order in your data. The issue with the BTI system is that the channel order is somewhat erratic (references ending up all over the place, and no nice alphabetical ordering of the magnetometer coils). Prepare_leadfield (the low-level function which computes the leadfield) just computes the solution to the forward model for the list of sensors in the input, the order of which is specified by the order in the data, or by the order in the gradiometer structure, if no data is supplied.</div><div>I recently (about a month ago) made a change in bti2grad, which changed the order of the coils in the grad-structure. Initially, I thought it would be nice to have them ordered alphabetically, but this led to problems later on when using precomputed leadfields (and making implicit assumptions about the matching sensor order in both data and gradiometers). It could be that your problems are related to this.</div><div>On the other hand: could this be replicated in other datasets? How many trials is your csd-matrix based on? Isn't there any hint of a bilateral temporal decrease in alpha activity?</div><div><br></div><div>Yours</div><div><br></div><div>Jan-Mathijs</div><div><br></div><div><br></div><div><br></div><div><div><div>On Nov 19, 2008, at 11:00 AM, Nathan Weisz wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">hi,<div><br></div><div>i'm not sure whether the following question is a fieldtrip-related question or a rather general question.</div><div><br></div><div>we use a 148 sensor BTI system.</div><div>since a couple of days we're struggling with a data-set in which we'd like to localize auditory cortical alpha desynchronizations. on a sensor level they are clearly observable (see attached Pitcure 2). however when running DICS it seems like the brain is more or less increasing power post-stimulus.</div><div>what makes me wonder is that it's exactly the same script (i could provide more details of course) which worked very successfully previously. our notion was initially that something is weird with the leadfield. but -illegally- testing it with a leadfield from another subject where things worked out basically gave more or less the same picture. now we assume that something is fishy with the data itself, that is not clearly observable when looking at the data on a trial-by-trial basis, leading to bad spatial filters. any suggestions how this could be diagnosed?</div><div><br></div><div>are there any other suggestions? or has anybody had similar problems lately?</div><div><br></div><div>cheers,</div><div>n</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><span><Picture 2.png></span></div><div><br></div><div><span><Picture 1.png></span></div><br><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; 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"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div><span class="Apple-style-span" style="font-weight: bold; ">--------------------------------------------</span></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 13px; "><b style="font-size: 13px; font-weight: bold; ">Dr. Nathan Weisz</b></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 13px; "><br class="khtml-block-placeholder"></span></font></div><div><i>OBOB-Lab</i></div><div>University of Konstanz</div><div>Department of Psychology</div><div>P.O. Box D23</div><div>78457 Konstanz</div><div>Germany</div><div><br></div><div><b style="font-weight: bold; ">Tel</b>: ++49 - (0)7531 - 88 45 84</div><div><b style="font-weight: bold; ">Email:<span class="Apple-converted-space"> </span></b><a href="mailto:nathan.weisz@uni-konstanz.de">nathan.weisz@uni-konstanz.de</a></div><div><b style="font-weight: bold; ">Homepage</b>: <a href="http://www.uni-konstanz.de/obob">http://www.uni-konstanz.de/obob</a></div><div><br></div><div><div>"Nothing shocks me. I'm a scientist." (Indiana Jones)</div></div></div></div></span></div></span></div></span></div></span></div></span></div></span></div></span> </div><br><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> </blockquote></div><br></div></div></blockquote></div><br></div><br><br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; 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"><div><div><span class="Apple-style-span" style="font-weight: bold; ">--------------------------------------------</span></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 13px; "><b style="font-size: 13px; font-weight: bold; ">Dr. Nathan Weisz</b></span></font></div><div><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 13px; "><br class="khtml-block-placeholder"></span></font></div><div><i>OBOB-Lab</i></div><div>University of Konstanz</div><div>Department of Psychology</div><div>P.O. Box D23</div><div>78457 Konstanz</div><div>Germany</div><div><br></div><div><b style="font-weight: bold; ">Tel</b>: ++49 - (0)7531 - 88 45 84</div><div><b style="font-weight: bold; ">Email:<span class="Apple-converted-space"> </span></b><a href="mailto:nathan.weisz@uni-konstanz.de">nathan.weisz@uni-konstanz.de</a></div><div><b style="font-weight: bold; ">Homepage</b>: <a href="http://www.uni-konstanz.de/obob">http://www.uni-konstanz.de/obob</a></div><div><br></div><div><div>"Nothing shocks me. I'm a scientist." (Indiana Jones)</div></div></div></div></span></div></span></div></span></div></span></div></span></div></span></div></span> </div><br></body></html><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>
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