[FieldTrip] planar gradients

[Eelke Spaak]

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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