[Eeglablist] re-referencing when online reference is a scalp channel

[Makoto Miyakoshi]

Hi Denise,

I agree with Joe. I recommend you keep that channel. That's the short
answer.

My long answer is as follows.

> If I simply apply the re-reference, I will still have 65 channels with 5Z
as an active channel. Should I remove the 5Z channel after re-referencing,
or is it better to retain it? What would be the best practice in this case?

Do you see flat data at 5Z right after recording? If yes, after applying
average reference, you'll see 65-ch non-zero time-series data, but your
data rank is 65-1=64. This 'clean' rank deficiency can be detected by ICA
etc. so no problem. But if you plan to apply matrix operations, you must
take care of it on your own (it will fail in an apparent way if you forget
to do so).

I discussed this re-reference issue in this paper. Joe is one of the four
experts I consulted (reported as 'private communication' in the paper) when
we wrote it. You might find it informative.
https://urldefense.com/v3/__https://www.frontiersin.org/journals/signal-processing/articles/10.3389/frsip.2023.1064138/full__;!!Mih3wA!C33pLXKR-yZpIxZJumzqIbkD7VqjPkgIswJtFpzXyFYmvgStiqdRbEBRym5oDsisnUOAE-5yGKmrqNu8K52-7YMKvt0$ 

Makoto

On Wed, Mar 26, 2025 at 12:35 AM Denise Dal Lago via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Hi all,
> I recorded EEG data using a 65-channel ANT Neuro cap with an online
> reference at channel 5Z (ANT Neuro labeling). I am now pre-processing the
> data in MATLAB with EEGLAB and need to re-reference to the common average.
> If I simply apply the re-reference, I will still have 65 channels with 5Z
> as an active channel. Should I remove the 5Z channel after re-referencing,
> or is it better to retain it? What would be the best practice in this case?
> I am more familiar with the Biosemi recording system, where I didn’t
> encounter this issue.
> Many thanks,
> Denise
>
>
>
> Denise Dal Lago, PhD
> Research Fellow
> Department of Psychology, University of Bologna
> Viale Berti Pichat, 5 -40127 Bologna, Italy
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