[Eeglablist] choice of reference

[Joseph Dien]

You might find the following paper helpful:

Dien, J. (1998). Issues in the application of the average reference: Review, critiques, and recommendations. Behavior Research Methods, Instruments, and Computers, 30(1), 34-43.

19-channels is a bit sparse for average reference but it also depends on how they are distributed on the head, not just the number.  It also depends on the ERPs you're interested.  The mastoids are definitely not electrically silent (they are located very close to the lateral temporal language areas).  There are also implications for statistical power of ANOVAs depending on the geometry of the ERP component dipolar field and the reference site.  It also depends on what kind of analyses you are planning on and also on how well known the ERP component is and whether you plan on making inferences about functional neuroanatomy, among other things.

Regarding noise, it depends on what kind of noise you're talking about.  Do you mean electrode noise (bad contacts that would only affect the one electrode) or background noise (coherent electrical fields influencing multiple electrodes that just happen to not be of interest, including EOG) or mechanical noise (movement artifacts affecting multiple electrodes caused by physical disturbances of the electrodes)?

Joe


On Jun 12, 2012, at 9:27 PM, Angel Tabullo wrote:

> Stephen, Lisandro and David: 
> 
> Many thanks for your prompt answers, you all have been very helpful!
> 
> 
> 
> De: Stephen Politzer-Ahles <politzerahless at gmail.com>
> Para: Angel Tabullo <angeltabullo at yahoo.com> 
> CC: "eeglablist at sccn.ucsd.edu" <eeglablist at sccn.ucsd.edu> 
> Enviado: Martes, 12 de junio, 2012 9:53 P.M.
> Asunto: Re: [Eeglablist] choice of reference
> 
> Hi Angel,
>  
> Steve Luck's book An Introduction to the Event-related potentials method has a lot of information on references and the consequences of  the reference you choose. A common issue with average reference is that it's best when you have a high-density cap with many channels, so it may not be a good reference to use with a 19-channel dataset. (I don't know if the amount of noise matters particularly for reference, but I don't have any experience myself using average reference--since I've only worked with low-density caps, I've never had a chance to use average reference).
>  
> Best,
> Steve
> 
> On Tue, Jun 12, 2012 at 11:36 AM, Angel Tabullo <angeltabullo at yahoo.com> wrote:
> Hello everyone! I wanted to ask if there's an advantage in using average reference over linked mastoids or earlobes when you are working with 19 channels and considerable levels of noise. Furthermore: can reference affect the SNR of an ERP? 
> 
> Thanks again for your attention and patience.
> 
> Angel Tabullo
> 
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> -- 
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://www.linguistics.ku.edu/
> 
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--------------------------------------------------------------------------------

Joseph Dien,
Senior Research Scientist
University of Maryland 

E-mail: jdien07 at mac.com
Phone: 301-226-8848
Fax: 301-226-8811
http://homepage.mac.com/jdien07/