[FieldTrip] create grad struct from headloc channels

[Eelke Spaak]

Hi Anne,

You mentioned that you used online head localization. For the
recording sessions that are split up amongst several data files, did
you reposition the subject to the original head position (i.e. the one
stored in the first data file)? If that is the case, then you should
be safe just using the gradiometer definition from the first data
file. If that's not the case, then indeed averaging the gradiometer
definitions makes sense. I don't think you need to explicitly deal
with the head position channels, though; you can just read in all the
grads using ft_read_sens and then average them together using
ft_average_sens.

Cheers,
Eelke

On Tue, 30 Jul 2019 at 05:54, Arjen Stolk <a.stolk8 at gmail.com> wrote:
>
> Hi Anne,
>
> Perhaps others can chime in since I lost the details on how to do this. It involves ft_headmovement and/or ft_average_sens, the latter of which you can find in the utilities folder. Have a look at those functions and see if you can figure it out from there in the meantime.
>
> Best,
> Arjen
>
> On Mon, Jul 29, 2019 at 7:35 PM Anne Urai <anne.urai at gmail.com> wrote:
>>
>> Hi FieldTrippers,
>>
>> My data have some sessions in which all trials are recorded in one CTF file, and others were participants took breaks in between blocks and there are several CTF files. For source reconstruction, I’d like to use each full session to have a similar number of trials per participant to estimate my common filter and apply a DICS beamformer.
>>
>> This means I’ll need to create a grad struct from my appended session files. As far as I understand, the grad struct for CTF is defined at the start of each recording session. In this case, we used online head localization, so it makes more sense to take the average gradiometer position from all trials (after epoching and artefact rejection) that remain in the data.
>>
>> Is there a way to compute a new grad struct from the headloc channels, after appending several recording files?
>>
>> Best,
>>
>> —
>> Anne E. Urai, PhD
>> Postdoctoral Fellow, Cold Spring Harbor Laboratory
>> www.anneurai.net / @AnneEUrai
>>
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