I want to use M1 and M2 as re-reference, the two electrodes have been marked as "EEG REF". Then in the “sensor types or names” place as shown in the attached picture, should I write "EEG" or "EEG REF"? Thank you!
Or I don't even need to mark M1 and M2 as "EEG REF", just regard all electrodes as "EEG"?
Sensor types or names, are the sensors that will be re-referrenced, so you need to write EEG
EEG reference channel(s) are the references to be used they can be channel names, this explicitly indicates the channels that will be used (e.g, M1, M2). Or they can be type (e.g., EEG REF), so all sensors that have this type will be used. In you case, this will lead to the same result, IFF only M1 and M2 are of the type EEG REF. For sake of clarity, prefer to write the channel names.
Note, the advantage of labelling as EEG REF is that these channels do not appear on the figures when EEG signals are plotted.
Dear Raymundo,
Thank you very much for your reply. Now I understand it quite well. Have a nice day.
Best regards,
Christina
Dear Raymundo,
How are you? I have another question concerning the order of "EEG reference" and "SSP: eye blinks". As shown in the attached pictures, you can see that applying the former or the latter first significantly changes the data. What might be the reason for it? What is the correct way of doing it? Thank you very much.
Best regards,
Christina
This should lead to very similar results. In most EGG pipelines re-referencing is performed before ICA- or SSP-based artifact removal.
From the first image, it seems that the SSP projector to remove blinks was computed after re-referencing was applied (it was selected). As such, even when you turn off the re-referencing in image2, the SSP projector is already computed on the re-referenced signals.
So, to make a fair comparison, you would need to:
Hello Raymundo, thank you very much for the reply. Now I know much better the right process to do it.
I followed these procedures and got the attached picture. But it seems that I don't have to worry too much about it. I just need to follow the correct procedure: re-referencing before SSP-based artifact removal, right? Thank your for the help.
For these, are M1 and M2 labelled as EEG channels?
If they are not, these two channels are not being affected by the SSP artifact removal (so, artifacts that are present in them will come back to the other EEG channels, when the other EEG channels are re-referenced to mastoids)
Correct.
Thanks a lot, Raymundo! Now I understand the logic and the right way of doing it. Have a nice day.
Sincerely,
Christina
