[Eeglablist] how can I rereference to average of ear electrodes

[Darren Weber]

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I have used a recording setup where all scalp electrodes were referenced
to A2.  In addition, A1 was recorded with reference to A2.  The purpose
for this was to avoid distortion of the EEG topography due to imbalances
in the electrode impedances across A1 and A2.  This is the general
problem of using a linked-ear reference.  If we recorded A1 with
reference to A2, we were able to simulate a linked-ear reference
off-line.  I have a perl script that we used for this, which has a small
help section to describe the simulation:

The primary application of the program is to correct a table of
124ch AERPs referenced to the right ear(re) by subtracting a
value equal to half of the left ear activity (le) which has been
referenced to the right ear.  This equates to a mathematically
balanced ear reference, according to the following formulation
for any given scalp site S:

(S-re)-0.5(le-re)
=S-re-0.5le+0.5re
=S-0.5(re+le)


This perl script is called 'mathears.pl' and it is in the perl module of
the cvs at http://eeg.sf.net

Best, Darren






Masaki Nishida wrote:
> Dear All,
> I have a similar problem regarding re-reference to average of both ear 
> electrodes.
> The montage of our recordings were C3-A2, C4-A1, O1-A2 and O2-A1.
> I have performed pop_reref with data with these four electrodes but data 
> after re-reference seemed quite
> similar prior to re-reference.
> 
> I would be grateful if anyone could tell me whether it could be possible to 
> re-reference to our data, and if impossible, how to arrange
> the montage of recordings in the future.
> 
> 
> Best wishes,
> Masaki Nishida
> 
> 
> 
> Masaki Nishida M.D.,Ph.D.
> 
> Department of Psychiatry, Center for Sleep and Cognition,
> Harvard Medical School, Beth Israel Deaconess Medical Center E/FD864
> 330 Brookline Ave. Boston, MA 02215
> phone: 617-667-8452 fax: 617-667-8498
> e-mail: mnishida at bidmc.harvard.edu
> 
> 
> 
> 
> 
> 
> 
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- --

Darren L. Weber, Ph.D.
Postdoctoral Scholar

Dynamic Neuroimaging Laboratory,
UCSF Department of Radiology,
185 Berry Street, Suite 350, Box 0946,
San Francisco, CA 94107, USA.

Tel: +1 415 353-9444
Fax: +1 415 353-9421
www: http://dnl.ucsf.edu/users/dweber

"To explicate the uses of the brain seems as difficult
a task as to paint the soul, of which it is commonly
said, that it understands all things but itself."
  Thomas Willis (The Anatomy of the Brain and Nerves, 1664)
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