<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Times New Roman; font-size: 12pt; color: #000000'>Hi Eelke,<br><br>Have you tried comparing the results with a time-domain beamformer? You could e.g. try LCMV on 15-25Hz-bandpassed data. This should give you in theory similar results.<br><br>Best,<br>Stan<br><br><br><br><hr id="zwchr"><blockquote style="border-left:2px solid rgb(16, 16, 255);margin-left:5px;padding-left:5px;"><b>Van: </b>"Eelke Spaak" <eelke.spaak@donders.ru.nl><br><b>Aan: </b>"FieldTrip discussion list" <fieldtrip@science.ru.nl><br><b>Verzonden: </b>Donderdag 21 november 2013 18:27:43<br><b>Onderwerp: </b>Re: [FieldTrip] Motor beta activity - DICS solution more noisy than sensor data?<br><br><p>Thanks for the input Vitória. Are you using Fourier input to sourceanalysis, or 'powandcsd'? I'm wondering whether the csd computation inside sourceanalysis might be to blame. Will investigate this tomorrow :)</p>
<p>Eelke</p>
<div class="gmail_quote">On Nov 21, 2013 6:01 PM, "Vitoria Piai" <<a href="mailto:v.piai.research@gmail.com" target="_blank">v.piai.research@gmail.com</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hi all, Eelke,<br>
<br>
Maybe adding to Eelke's remark, although I'm not working with motor beta activity and lateralised index.<br>
I'm also using DICS and my very clear, focal sensor-level effects all of a sudden become localised to the whole brain or a whole hemisphere!<br>
I happen to have heard from Jan-Mathijs that there may something going on at the moment, but at least for now, Eelke, I don't think this error is unique to our data (and I was actually going to post my incompatible sensor-source results here soon, so now it's less work for me :)<br>
<br>
Looking forward to hearing your updates,<br>
(I'm interrupting my source-level analyses for the time to get a better feeling for the sensor-level data first)<br>
Vitória<br>
<br>
On 21-11-2013 17:36, Eelke Spaak wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Fellow FieldTrippers,<br>
<br>
Currently I am looking at a contrast for left- versus right-hand index<br>
finger button presses. As expected, on sensor level (combined planar<br>
gradient, grand average) I see a clear lateralisation in beta band<br>
power starting at least 0.5s before the button press (see<br>
<a href="https://db.tt/Rtch3Qjy" target="_blank">https://db.tt/Rtch3Qjy</a>). Both 'blobs' are significant; there is<br>
clearly more beta power ipsilateral to the response hand. I would<br>
prefer to do further analyses on source level, so I attempt to<br>
reconstruct the sources for this effect using DICS beamformer (common<br>
filter, applied to both conditions separately; fixedori and realfilter<br>
= 'yes'). The grand average results for this (again contrast left vs<br>
right response hand) are shown at <a href="https://db.tt/IBQZG0d8" target="_blank">https://db.tt/IBQZG0d8</a> . (Ignore the<br>
R/L-flip, this is radiological convention.)<br>
<br>
As you can see, the source level solution is much more blurry than on<br>
sensor level. This picture is without using any regularisation (lambda<br>
parameter), the results are even worse when I use lambda = '5%'. The<br>
negative blob (right hand higher power than left) becomes 'marginally<br>
significant' on source level (p ~ 0.06) where it was p < 0.001 on<br>
sensor level. The positive blob is nowhere near significant. Also, the<br>
individual results are much less topographically consistent on source<br>
than on sensor level (explaining the worse statistics).<br>
<br>
I have checked the segmentation of my MRIs, the 'gray' seems to be<br>
nicely within the head all the time. Also, I have manually verified<br>
the alignment of headmodel, sourcemodel, and gradiometer information<br>
for all subjects.<br>
<br>
As a final note, the above sensor-level plot was taken from a 'slice'<br>
out of a planar-gradient time-frequency analysis (mtmconvol). The<br>
ingredient for the beamformer was an mtmfft fourier spectrum on the<br>
axial gradiometer data, obtained for just the time-frequency range of<br>
interest (subselect toilim [-0.5 0], mtmfft foi = 23, tapsmofrq = 7).<br>
When I compute condition-averaged power based on these fourier spectra<br>
and look at the contrast, the results are again as expected:<br>
<a href="https://db.tt/n2P3UKcQ" target="_blank">https://db.tt/n2P3UKcQ</a> (of course less localised because of axial<br>
gradient vs planar). The freq structures underlying this contrast are<br>
exactly the same as those going into ft_sourceanalysis, so the problem<br>
must be in the source analysis step (and/or in the preparation of the<br>
geometric information, although these seem fine by visual inspection).<br>
<br>
Does anyone have any idea that might explain these seemingly<br>
contradictory results? I would have expected demixing to improve<br>
signal-to-noise ratio, rather than worsen it.<br>
<br>
Thanks!<br>
Best,<br>
Eelke<br>
______________________________<u></u>_________________<br>
fieldtrip mailing list<br>
<a href="mailto:fieldtrip@donders.ru.nl" target="_blank">fieldtrip@donders.ru.nl</a><br>
<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip" target="_blank">http://mailman.science.ru.nl/<u></u>mailman/listinfo/fieldtrip</a><br>
</blockquote>
<br>
<br>
-- <br>
Vitória Piai<br>
PhD Candidate<br>
Donders Institute for Brain, Cognition and Behaviour<br>
Centre for Cognition, Radboud University Nijmegen<br>
Montessorilaan 3, B.01.05<br>
6525 HR Nijmegen<br>
The Netherlands<br>
<br>
Email : <a href="mailto:V.piai@donders.ru.nl" target="_blank">V.piai@donders.ru.nl</a><br>
Phone : <a href="tel:%2B31%2024%203612635" target="_blank">+31 24 3612635</a><br>
<a href="http://www.vitoriapiai.com" target="_blank">www.vitoriapiai.com</a><br>
<br>
______________________________<u></u>_________________<br>
fieldtrip mailing list<br>
<a href="mailto:fieldtrip@donders.ru.nl" target="_blank">fieldtrip@donders.ru.nl</a><br>
<a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip" target="_blank">http://mailman.science.ru.nl/<u></u>mailman/listinfo/fieldtrip</a><br>
</blockquote></div>
<br>_______________________________________________<br>fieldtrip mailing list<br>fieldtrip@donders.ru.nl<br>http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</blockquote><br><br><br>-- <br><div><span name="x"></span>
<meta http-equiv="Content-Type" content="text/html; charset=Windows-1252">
<meta name="Generator" content="MS Exchange Server version 08.00.0681.000">
<title></title>
<!-- Converted from text/plain format -->
<p><font size="2">Stan van Pelt, PhD<br>
Donders Institute for Brain, Cognition and Behaviour<br>
Centre for Cognition<br>
Montessorilaan 3, B.01.19<br>
6525 HR Nijmegen<br>
tel: 024-3616288</font>
</p>
<span name="x"></span><br></div></div></body></html>