[FieldTrip] CTF275 MEG channel position from FieldTrip to EEGLAB

[Zhi Li]

Hi Jan-Mathijs,

Many thanks for your kind reply. I have solved this problem by adding the
ctf275 channel type to the source code for data reading. I'd like to use
IClabel which is a plugin of EEGLAB to label the components automatically.

Best wishes,

Zhi Li

On Wed, 6 Jul 2022 at 12:01, Schoffelen, J.M. (Jan Mathijs) via fieldtrip <
fieldtrip at science.ru.nl> wrote:

> Hi Zhi Li,
>
> I am unfamiliar with the way in which EEGLAB deals with sensor/electrode
> positions, and how these are read from the data file.
>
> On the other hand it is unclear to me what your actual problem is. Is it
> only a matter of visualization (because for ICA the sensor positions are
> not needed)? Have you checked the EEGLAB documentation?
>
> Since you are asking for another solution: you can also do the ICA in
> fieldtrip, there’s no need to go to eeglab for that.
>
> Best wishes,
> Jan-Mathijs
>
>
> On 30 Jun 2022, at 22:07, Zhi Li via fieldtrip <fieldtrip at science.ru.nl>
> wrote:
>
> Hi,
>
> I would like to use ICA and IClabel in EEGLAB to detect artefacts in my
> MEG data. But no matter if I used *fieldtrip2eeglab* or *pop_fileio*, the gradiometer
> channel positions cannot be correctly extracted from the ctf275 .ds folder.
> The channel positions in eeglab format *EEG* are all empty.
>
> I tried to copy the channel information directly from the header of the
> ctf275 data folder but the MEG channels cannot be projected on the 2-D map
> appropriately. It seems like the channel position in the MEG data imported
> by FieldTrip are the real locations of the MEG helmet and their unit is cm.
> whereas the channel position in EEGLAB is based on the 10-10 system which
> is already on the scalp. Hence the projected channels on the scalp are all
> misplaced if I use the raw XYZ from the header of ctf275 data.
>
> May I ask how I could transform the MEG channel position from FieldTrip to
> EEGLAB appropriately, or is there any other solution? Many thanks.
>
> Best regards,
>
> Zhi Li
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