<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Maité,<div><br></div><div>What do you mean by spatially not located sources?</div><div>In general it may be helpful to give more to-the-point information besides the input cfg-structures. The output of your beamformer analysis depends both on the sanity of the data (which I cannot check), and on the sanity of the input configuration.</div><div>Two remarks w.r.t the cfg:</div><div><br></div><div>-when cfg.lambda is a scalar, the csd-matrix will be regularized with an identity matrix, scaled with cfg.lambda. From your value of 0.05 however I assume that you want to do a relative scaling. True? In that case you should specify cfg.lambda = '5%'; The consequence of the 0.05 could be that if the scale of your data is Volts-squared or microVolts-squared (boiling down to the csd having a magnitude of 10^-12 or 1, respectively) which at least in the first case leads to inappropriate regularisation.</div><div>-in the second step I assume you want to re-use the filters computed in step 1. Therefore you need to pass source.avg.filter (computed in the first step) to the cfg. Does this happen in source2grid? I don't know, it could be, but I'd check that if I were you.</div><div><br></div><div>Some post-processing probably needs to be done in order to see spatially localized sources (even when the whole analysis went fine (=data OK and cfgs OK) until this point), so just looking at the output of sourceanalysis typically is not optimal.</div><div><br></div><div>For the computation of the CSD-matrix I'd like to refer to the tutorial <span class="Apple-style-span" style="font-family: 'Lucida Grande', Arial, Verdana, sans-serif; font-size: 13px; line-height: 19px; "><a href="http://fieldtrip.fcdonders.nl/tutorial/beamformer">http://fieldtrip.fcdonders.nl/tutorial/beamformer</a></span></div><div>on the fieldtrip wiki.</div><div><br></div><div>Best,</div><div><br></div><div>Jan-Mathijs</div><div><br></div><div><br><div><div>On Jul 6, 2010, at 12:56 PM, Maite Crespo wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Hello!<br><br>I read some previous mails in the discussion list, but I'm still not sure about <br>the procedure I'm following. I'm obtaining too flat images (not spatially located <br>sources). I would like to localize the source activity within a frequency band <br>and a time window. I computed the CSD matrix using ft_freqanalysis. Can I <br>average the resulting matrix in frequency and time before using it with <br>ft_sourceanalysis? <br><br>I used the following steps to compute the filters in the averaged CSD (across <br>trials) and then apply it to compute the power in single trial data. Is that <br>right? <br><br>% 1st run<br>cfg=[];<br>cfg.frequency=5;<br>cfg.latency=.7;<br>cfg.method='dics';<br>cfg.projectnoise='yes';<br>cfg.keepfilter='yes';<br>cfg.grid=grid;<br>cfg.vol=vol;<br>cfg.elecfile=elecfile;<br>cfg.lambda=.05;<br>source=ft_sourceanalysis(cfg,data);<br><br>% 2nd run<br>cfg=[];<br>cfg.frequency=5;<br>cfg.latency=.7;<br>cfg.method='dics';<br>cfg.projectnoise='yes';<br>cfg.rawtrial='yes';<br>source.leadfield=grid.leadfield;<br>cfg.grid=source2grid(source);<br>cfg.vol=vol;<br>cfg.elecfile=elecfile;<br>cfg.lambda=.05;<br>source=ft_sourceanalysis(cfg,data);<br><br>I also tried changing the lambda parameter, but it seems there are not many <br>changes...<br><br>Many thanks in advance for any help.<br><br>Best regards,<br>Maité<br><br>----------------------------------<br>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. See also <a href="http://listserv.surfnet.nl/archives/fieldtrip.html">http://listserv.surfnet.nl/archives/fieldtrip.html</a> and <a href="http://www.ru.nl/neuroimaging/fieldtrip">http://www.ru.nl/neuroimaging/fieldtrip</a>.<br><br></div></blockquote></div><br><div apple-content-edited="true"> <div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Dr. J.M. (Jan-Mathijs) Schoffelen </div><div>Donders Institute for Brain, Cognition and Behaviour, <br>Centre for Cognitive Neuroimaging,<br>Radboud University Nijmegen, The Netherlands</div><div><a href="mailto:J.Schoffelen@donders.ru.nl">J.Schoffelen@donders.ru.nl</a></div><div>Telephone: 0031-24-3668063</div></div> </div><br></div></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>
<p> http://www.ru.nl/fcdonders/fieldtrip/</p>