ctf data / 3rd gradients and megplanar/combineplanar

Michael Wibral wibral at BIC.UNI-FRANKFURT.DE
Wed Aug 19 12:35:28 CEST 2009

Dear Listusers,

we have stumbled over a little thing in relation to ctf MEG data and the new preprocessing tools for 3rd gradients. This is not an error in the code, but something that the users can easily do wrong:

Combineplanar gives strange results if the ctf reference channels are still in the data, but doesn't really throw an error (in FT20081210, FT ??). Note that - to my limited knowledge - you need the ctf reference channels (P,Q,R,B,G, etc.) in preprocessing if you want to use the ctf tools and synthetic 3rd gradient formation (or want to backtransform from 3rd gradients to magnetometers). Therefore you have to take care to finally get rid of these channels at some point before you compute megplanar or combineplaner. A typical point in your code to do this would be after 3rd gradient preprocessing and before filtering or any other preprocessing. Simply set cfg.channel={'MEG'} for this next step.

Hope this helps,

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 http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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