[FieldTrip] CTF275 MEG channel position from FieldTrip to EEGLAB

[Schoffelen, J.M. (Jan Mathijs)]

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<mailto: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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