[Eeglablist] Question about AVG referencing

[장진원]

Dear Enrico,

Practically, I do average reference after removing all non-scalp channels.
This includes the initial reference (ear mastoids, for example)

Sincerely,
Jinwon
On Wed, Jul 22, 2026 at 4:09 PM Enrico Fratto via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Greetings to all the community.
>
> I am reaching out to ask about something which is often overlooked but
> sometimes clicks hard to understand for me as the average reference
> process.
> Let's say I have 22 channels + Fz which is used as the reference.
>
> According to Makoto's famous explanation (
>
> https://eeglab.ucsd.edu/wiki/Makoto%27s_preprocessing_pipeline?source=post_page---------------------------&utm_source=chatgpt.com#Re-reference_the_data_to_average_(10/31/2025_Updated) 
> )
> we are supposed to add a 0 line in the AVG reference calculation to account
> for the reference channel itself (corresponding to dividing the sum at the
> n electrodes by n+1 to encompass the reference) when the flat channel is
> not already present in the data.
> In my case, it would be the sum at the 22 recording electrodes divided by
> 23 to encompass Fz.
> My question now is: let's say I acquired EEG with a reference I am not
> interested in (say, extra-cephalic). Would I still have to encompass it in
> the denominator while calculating the AVG in this case? Or, because it is
> not part of the head, I treat it as if it does not belong to the
> "zero-potential" assumption and I just estimate the average using the
> remaining electrodes?
> And what should I do instead if the reference is at another cephalic custom
> location (not belonging to the standard electrodes)?
>
> Thank you in advance for your help,
>
> Best
>
>
> --
> Enrico Fratto, MD
> Neuroscience Research Center, Department of Medical and Surgical Sciences
> Institute of Neurology, Department of Medical and Surgical Sciences
> University Magna Graecia,
> Viale Europa, 88100, Catanzaro, Italy
> <https://urldefense.com/v3/__https://www.google.com/maps/search/Viale*Europa,*88100,*Catanzaro,*Italy?entry=gmail&source=g__;KysrKw!!Mih3wA!Adb9bcTf-SV95Gi4QAMI44I6_1CtbEmYJ-4s5M-DcW8DDVgwlYNxaHnf5HG-SLqhotxXf_gqF0oMbJIt0FW7Ihyhow$ >
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