combineplanar for 275-ch CTF data

jan-mathijs schoffelen jan.schoffelen at FCDONDERS.RU.NL
Tue Dec 4 14:44:35 CET 2007


Dear Dasha,

In order to compute the planar gradient of the magnetic field at the
position of a given axial gradiometer, you always have to take the
axial gradient of the magnetic field, measured by a bunch of
neighbouring gradiometers, into account. I guess that the order in
which you want to do things does not make sense in this context.
First, you select a subset of sensors, and then you transform to the
planar gradient. I would call megplanar without the subset of
channels, and only select the subset of channels after having called
combineplanar.

Yours,

Jan-Mathijs

On Dec 4, 2007, at 2:25 PM, Daria Osipova wrote:

> Hi
> I am trying to analyze 275-channel data but having trouble with
> combineplanar. I want to calculate planar gradient for posterior
> channels only (86 channels) and here's my configuration:
> cfg = [];
> cfg.channel = channelselection({'MLO', 'MRO', 'MRP', 'MLP', 'MZP',
> 'MZO'}, data.label);
> cfg.planarmethod = 'sincos';
> data_planar = megplanar(cfg, data);
> comb =combineplanar([], data_planar);
>
> data_planar.label contains 361 channels i.e. it includes 86*2=172
> channels for which planar gradient has been calculated and the rest
> of the channels in the original non-planar form.
>
> When I use combineplanar, I get 322 channels some of which are the
> orginal non-planar channels, some are the result of the combined
> planar gradient and some are not combined planar gradient.
> I suspect this has something to do with checking for the layout
> (151 or 275 channels) since the same scheme seems to work ok for
> the old 151 -channel dataset.
> Thanks in advance.
> Bests, Dasha
>
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> 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/
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>

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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/fcdonders/fieldtrip.



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