[Eeglablist] Reference to linked mastoids - Neuroscan

Tara Davis taradavis001 at gmail.com
Wed Mar 15 07:44:15 PDT 2017

Hi all,

I usually use a 64 channel cap with averaged mastoids as my reference.
Regrettably, I recently obtained pediatric 20 channel caps and learned
afterwards that they have linked mastoids. I would return them for unlinked
mastoids, but I've already lost a lot of time on this project.

I've been unable to get EEGLAB to recognize the linked electrodes as the
reference. M1 & M2 were not present in the channel locations.  I used the
M1-M2 channel locations from my 64 channel file to append these channel
locations in EEGLAB (added channels 21 & 22).  Then I tried to reference
the mastoids in 2 ways:

1. From the GUI: I clicked on Re-reference data to channels, retain old
reference channels in data and add current reference channel back to data.
M1-M2 were available.  However, when I added them, I received an error
message, "Aborting - you must enter one or more reference channels."

2. I also tried entering the following from the command line:
EEG = pop_reref (EEG, [21,22], 'keepref', 'on');

I have two questions.  (1) Is there anyway to troubleshoot this problem?
(2) If I can't fix it, will it be a problem that the reference will be
unknown for ICA, even though there was a reference when the data was

Tara Davis

Tara M. Davis, Ph.D. CCC-A
University of South Alabama
Associate Professor
Department of Speech Pathology & Audiology
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