<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi Jan, Tom and the rest,<div><br></div><div>I agree with Tom, but would like to strongly emphasize that differences in power across conditions more often than not will affect the coherence landscape in a non-trivial way. This does not only count for power changes in the reference dipole, but also for changes in power for third party dipoles (i.e. any potential other source). Therefore the interpretation of the subtracted coherence volumes should be done with care.</div><div><br></div><div>BW,</div><div><br></div><div>JM</div><div><br><div><div>On Dec 2, 2011, at 6:52 PM, Tom Holroyd (NIH/NIMH) [E] wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>The solution I have adopted is to always look at coherence contrasts. Make two volumes using the same reference dipole in two different conditions, then subtract the volumes. The self-coherence of the reference will disappear. Mostly. Then use stats, like a U-test.<br><br><a href="mailto:Jan.Hirschmann@med.uni-duesseldorf.de">Jan.Hirschmann@med.uni-duesseldorf.de</a> wrote:<br><blockquote type="cite">Hi community,<br></blockquote><blockquote type="cite"> Regarding this thread on suppressing the reference dipole from 2004, what is the current status? Has anybody found and implemented a recommendable way to project out activity from unwanted dipoles? Thank you for any comments/opinions!<br></blockquote><blockquote type="cite"> Best,<br></blockquote><blockquote type="cite">Jan Hirschmann<br></blockquote><blockquote type="cite"> On 21 Oct 2004, at 17:23, Tom Holroyd wrote:<br></blockquote><blockquote type="cite"> <br></blockquote><blockquote type="cite"><blockquote type="cite">/ When running a coherence volume using a reference dipole, one/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ naturally expects the coherence will be high around the reference/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ dipole./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ This effect tends to dominate the images./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Is there a way to normalize the coherence volume to eliminate/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ this effect? Perhaps by dividing by the coherence in a "control"/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ state?/<br></blockquote></blockquote><blockquote type="cite"> Hi Tom,<br></blockquote><blockquote type="cite"> The dominating effect of the refdip is indeed very problematic. I just<br></blockquote><blockquote type="cite">happened to have discussed this with Joachim Gross, and I have included<br></blockquote><blockquote type="cite">our email exchange below. Please first read that ...<br></blockquote><blockquote type="cite"> Basically I agree with Joachim, and I don't trust the supdip that is<br></blockquote><blockquote type="cite">implemented in FieldTrip's sourceanalysis function. Better test and map<br></blockquote><blockquote type="cite">the significance of the difference in coherence between two conditions<br></blockquote><blockquote type="cite">using randomization of the trials before the coherence is beamed (that<br></blockquote><blockquote type="cite">is implemented in sourceanalysis + sourcestatistics).<br></blockquote><blockquote type="cite"> Robert<br></blockquote><blockquote type="cite"> --------------------------------------------------------------------<br></blockquote><blockquote type="cite">my question to Joachim was<br></blockquote><blockquote type="cite">----------------------------------------------------------------------<br></blockquote><blockquote type="cite"> Begin forwarded message:<br></blockquote><blockquote type="cite"> <br></blockquote><blockquote type="cite"><blockquote type="cite">/ From: Robert Oostenveld <//roberto at <a href="http://smi.auc.dk">smi.auc.dk</a> <<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a>>//>/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Date: 1 October 2004 10:26:02 GMT+02:00/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ To: Joachim Gross <//jgross at <a href="http://uni-duesseldorf.de">uni-duesseldorf.de</a> <<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a>>//>/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Subject: dipole suppression/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Hi Joachim,/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ What I always still had to ask you is how you do supression of dipoles/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ in DICS, especially in the case of coherence imaging. I have thought/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ of two ways of projecting them out:/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ 1) compute supdip leadfield and its projection on the COV/CSD matrix,/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ then project it out of the COV/CSD matrix (which looses 2 or 3 from/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ its rank)./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ 2) compute supdip leadfield and add it to the leadfield of the dipole/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ with which is scanned (scandip). Subsequently compute the source/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ COV/CSD on those 6 leadfield components and select the 3x3 submatrix/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ that corresponds with the scandip to continue the computations with./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Both methods don't really gave me very convincing results. A third/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ approach would be to add the supdip leadfield to the (identity) noise/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ matrix and project it through the filters. Then nai=pow/noise is/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ corrected for the presence of the supdip, but that does not result in/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ a supressed source coherence distribution. What is your idea or/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ approach for this?/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ best regards/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Robert/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"> ----------------------------------------------------------------------<br></blockquote><blockquote type="cite">and his answer (Joachim, I hope you don't mind me sharing this on the<br></blockquote><blockquote type="cite">list)<br></blockquote><blockquote type="cite">----------------------------------------------------------------------<br></blockquote><blockquote type="cite"> Begin forwarded message:<br></blockquote><blockquote type="cite"> <br></blockquote><blockquote type="cite"><blockquote type="cite">/ From: Joachim Gross <//jgross at <a href="http://uni-duesseldorf.de">uni-duesseldorf.de</a> <<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a>>//>/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Date: 14 October 2004 17:20:45 GMT+02:00/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ To: "//robert.oostenveld at <a href="http://fcdonders.kun.nl">fcdonders.kun.nl</a> <<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a>>//"/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ <//robert.oostenveld at <a href="http://fcdonders.kun.nl">fcdonders.kun.nl</a> <<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a>>//>/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Subject: dipole suppression/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Hi Robert,/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ sorry for the delay./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ The dipole suppression is indeed a complex issue./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ We first implemented it because it facilitates visualization and the/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ exact identification of the first/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ strongest local maxima./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Nevertheless, it is quite dangerous because the map is (locally)/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ distorted in a non-trivial way./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ We are now trying to move away from suppressing the sources. I think/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ it would be better to identify the/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ significant local maxima (significance based on/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ randomization/permutation)./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ But what we are doing at the moment is your approach 3./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ So we add the supdip leadfield to the noise covariance matrix and look/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ at pow/noise./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ For coherence we are basically doing the same thing./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ So we divide the coherence map (or actually the map of cross spectral/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ densities) by a noise map/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ that peaks at the locations of the "unwanted" dipoles./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ With this procedure we loose absolute coherence values./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ This is not so important for us since we get the absolute values from/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ the coherence and partial coherence spectra/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ that are computed afterwards./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ It works surprisingly well but should be used with care./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ A better approach would be to map partial coherence (with the unwanted/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ dipoles removed). But we have not implemented/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ this so far./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Again, I think it is better to have regions of interest identified by/<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ their significance./<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ /<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">/ Joachim/<br></blockquote></blockquote><blockquote type="cite"> ----------------------------------------------------------------------<br></blockquote><blockquote type="cite">Robert Oostenveld, PhD<br></blockquote><blockquote type="cite">Center for Sensory-Motor Interaction (SMI)<br></blockquote><blockquote type="cite">Aalborg University, Denmark<br></blockquote><blockquote type="cite"> and<br></blockquote><blockquote type="cite"> F.C. Donders Centre for Cognitive Neuroimaging<br></blockquote><blockquote type="cite">University Nijmegen<br></blockquote><blockquote type="cite">P.O. Box 9101<br></blockquote><blockquote type="cite">NL-6500 AH Nijmegen<br></blockquote><blockquote type="cite">The Netherlands<br></blockquote><blockquote type="cite"> Tel: +31 (0)24 3619695<br></blockquote><blockquote type="cite">Fax: +31 (0)24 3610989<br></blockquote><blockquote type="cite">----------------------------------------------------------------------<br></blockquote><blockquote type="cite">N.B. Starting from 1 September 2004, the University of Nijmegen has<br></blockquote><blockquote type="cite">changed its name to Radboud University Nijmegen. All web- and<br></blockquote><blockquote type="cite">email-addresses ending in ".kun.nl" should therefore be changed into<br></blockquote><blockquote type="cite">".ru.nl". Please update your address book and links.<br></blockquote><blockquote type="cite"> Jan Hirschmann<br></blockquote><blockquote type="cite">MSc. Neuroscience<br></blockquote><blockquote type="cite">Insititute of Clinical Neuroscience and Medical Psychology<br></blockquote><blockquote type="cite">Heinrich Heine University Duesseldorf<br></blockquote><blockquote type="cite">Universitaetsstr. 1<br></blockquote><blockquote type="cite">40225 Duesseldorf<br></blockquote><blockquote type="cite">Tel: 0049 - (0)211 - 81 - 18415<br></blockquote><blockquote type="cite"> ------------------------------------------------------------------------<br></blockquote><blockquote type="cite">_______________________________________________<br></blockquote><blockquote type="cite">fieldtrip mailing list<br></blockquote><blockquote type="cite"><a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a><br></blockquote><blockquote type="cite"><a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a><br></blockquote><br>-- <br>"The test of a first-rate intelligence is the ability to hold two<br>opposed ideas in the mind at the same time, and still retain the<br>ability to function." — F. Scott Fitzgerald<br>_______________________________________________<br>fieldtrip mailing list<br><a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a><br>http://mailman.science.ru.nl/mailman/listinfo/fieldtrip<br></div></blockquote></div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-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: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-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: 0px; font-size: medium; "><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-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-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: 0px; font-size: medium; "><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-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; font-size: medium; "><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-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; font-size: medium; "><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: medium; 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>Jan-Mathijs Schoffelen, MD PhD </div><div><br></div><div>Donders Institute for Brain, Cognition and Behaviour, <br>Centre for Cognitive Neuroimaging,<br>Radboud University Nijmegen, The Netherlands</div><div><br></div><div>Max Planck Institute for Psycholinguistics,</div><div>Nijmegen, The Netherlands</div><div><br></div><div><a href="mailto:J.Schoffelen@donders.ru.nl">J.Schoffelen@donders.ru.nl</a></div><div>Telephone: +31-24-3614793</div></div></span></div></span></div></span></div></span></div></span></span>
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