Adding EEG positions template for multiple files in group analysis

1

Hi

For my analysis with multiple subjects I used Biosemi 128 channels. My raw files have 144 channels (128 main electrodes + additional channles; EXG 1-8, GSR1-2, etc). I didn't record any data on these additional channels, just on the 128 channels.

Under protocol > group analysis > common files, I added the Biosemi 128 A1 template. When I add/review individual raw files, this template isn't automatically added to their raw file and I can't view topography, presumably due to mismatch in number of channels.

When I right-click 'BDF channels (144)' on each individual raw file and add the Biosemi 128 A1 template it seems to work. I get a message '128 channels updated, 8 channels not found' and the topography/sensor positioning looks fine. Is there a way to set this template as a default for all files so it's automatically added when the raw file is imported rather than having to add it for each individual file?

2

Hi David,

You can change the properties of subjects (including the Group analysis subject) so that all recordings of this subject share the same channel file. To do so, right click on the subject -> Edit subject -> Yes, use one channel file per subject. You can also apply EEG position templates to existing recordings using the Add EEG positions process under Import -> Channel file.

I hope this helps,
Martin

3

If you are using ICA or SSP cleaning, I don't recommend using a common channel file shared per subject (and never share a channel file across subjects).
I'd recommend the other approach Martin mentioned: select all the raw files in the protocol (you can select directly a subject folder in the Process1 list, or even the entire protocol) and run the process "Add EEG positions".

4

Thank you.