[FieldTrip] Fwd: planar gradients

[Eelke Spaak]

Dear Fred and Max,

To follow up on this: we have identified and fixed the problem, as of last
night's release. You can see the issue here:
http://bugzilla.fcdonders.nl/show_bug.cgi?id=1858 This is a related, but
different, bug than the 1288 I posted earlier.

To summarize: all output of ft_megplanar should now be recognized correctly
as planar gradient data in subsequent steps. If you have data that was
generated by ft_megplanar prior to this fix, you can easily patch it by
doing:

data.grad.type = 'ctf275_planar';

(or xxxx_planar for other axial gradiometer acquisition systems).

Feel free to reopen bug 1858 if the issue has not been resolved.

Best,
Eelke


On 23 November 2012 09:48, Eelke Spaak <eelke.spaak at donders.ru.nl> wrote:

> Dear Fred and Max,
>
> This is a known bug in ft_senstype, and people are working on fixing
> it. See bugzilla: http://bugzilla.fcdonders.nl/show_bug.cgi?id=1288 .
> If you have anything to add to the bug reports over there, that could
> be helpful.
>
> For now, Max's workaround seems to do the trick.
>
> Best,
> Eelke
>
> On 22 November 2012 19:36, Stenner, Max-Philipp
> <max-philipp.stenner at med.ovgu.de> wrote:
> > Dear Fred,
> >
> > I encountered a similar problem with my CTF275 data and one broken
> sensor before ft_freqanalysis of the planar (uncombined) data. "Confirming"
> the channel type with
> >
> > data.grad.chantype = ft_senstype(data);
> >
> > solved the problem (although I have to admit that I never investigated
> where in the ft script the problem arose).
> >
> > Cheers,
> > Max
> >
> > ________________________________________
> > Von: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl]"
> im Auftrag von "Frederic Roux [f.roux at bcbl.eu]
> > Gesendet: Donnerstag, 22. November 2012 14:19
> > Bis: FieldTrip discussion list
> > Betreff: [FieldTrip] planar gradients
> >
> > Dear all,
> >
> > I would like to follow up this post with another question
> > related to the planar gradients.
> >
> > I am working on data aquired with a CTF 275 system but at
> > the time of the acquisition there was a number of sensors
> > that were broken.
> >
> > So I end up with n = 258 channels.
> >
> > After running the ft_megplanar function I get n = 516 channels.
> >
> > However, if I try to combine the gradients with
> > ft_combineplanar
> >
> > I get an error saying that I am not providing ctf275_planar but
> > ctf275 data.
> >
> > Is the fact that I do not have n = 275 sensors but 258 confusing
> > the ft_combineplanar function, or is this related to something else?
> >
> >
> > Best,
> >
> > Fred
> >
> > ----- Original Message -----
> > From: "Eelke Spaak" <eelke.spaak at donders.ru.nl>
> > To: "FieldTrip discussion list" <fieldtrip at science.ru.nl>
> > Sent: Wednesday, November 21, 2012 12:47:25 PM
> > Subject: Re: [FieldTrip] ft_freqstatistics tutorial question
> >
> > Dear Nenad,
> >
> > Strictly speaking, planar gradient transformation is not necessary, so
> > you can just skip those steps if you really want to. However, if you
> > have axial gradiometer data (as I seem to recall from your earlier
> > posts) and want to do TF-analysis and -statistics on sensor level, I
> > would strongly recommend applying a planar gradient transformation.
> >
> > Axial gradiometer data will produce maximal deflections (of opposite
> > polarity) on both sides of a current dipole, while planar gradiometer
> > data produces a positive maximum exactly above the source. If you
> > apply TF-analysis to axial gradiometer data, you will get two
> > spatially separated 'blobs' where there was only a single oscillating
> > dipole in the brain. If you look at power (as is typically done), you
> > will lose the polarity information, and hence interpreting the power
> > topography in terms of brain is nearly impossible with axial gradient
> > data.
> >
> > Best,
> > Eelke
> >
> > On 21 November 2012 11:30, Nenad Polomac <polomacnenad at gmail.com> wrote:
> >> Dear all,
> >>
> >> I have one doubt. I want to calculate ft_freqstatistics on my MEG date
> >> obtained form  ft_freqanalysis. However, I see now in ft_freqstatistics
> >> tutorial that you suggest that operation should be done on planar
> gradient
> >> data. So, the first  ft_megplanar and then ft_freqanalysis,
> ft_combineplanar
> >> and ft_freqstatistics. My question is, does this step of calculating
> planar
> >> gradients for time frequency analysis is necessary or not? Could I apply
> >> statistic on the data from ft_freqanalysis without any involvement of
> planar
> >> gradients calculation.
> >> Thank you in advance!
> >>
> >> All the best!
> >>
> >> Nenad
> >>
> >>
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> >> fieldtrip at donders.ru.nl
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