[Eeglablist] EEG reference BioSemi system

[Steve Luck]

Hi Estelle.  The choice of reference electrode is not simple.  Any reference choice has both benefits and drawbacks.  The best advice is usually to look at your data with a few different references.  The most common choices are the average of all the electrodes and the average of the mastoids or earlobes.  The average of all sites is usually appropriate only if you have a large number of equally spaced electrodes that cover much of the head (see Dien, J. (1998). Issues in the application of the average reference: Review, critiques, and recommendations. Behavior Research Methods, Instruments & Computers, 30, 34-43).  Also, the waveform you get at a given electrode site with the average reference will depend on what electrodes you are recording from, so your waveforms may look different from those of another laboratory that also uses the average reference (if they use a different overall set of electrodes).

Cz is commonly used as reference in some specific areas.  And the tip of the nose is also used in some areas.  

A detailed discussion can be found in Chapter 3 of my book on ERP methods (An Introduction to the Event-Related Potential Technique, MIT Press).

Steve Luck

> From: Estelle Longin <estellelongin at gmail.com>
> Subject: [Eeglablist] EEG reference BioSemi system
> Date: January 10, 2012 3:24:37 AM PST
> To: <eeglablist at sccn.ucsd.edu>
> 
> 
> Dear collegues,
> 
> I am new in EEG analyses so I apologize if my question seem trivial.
> I am working on data recorded with a 128 high-density cap (BioSemi system); no specific reference electrode was used during the recording.
> I am wondering what is the best reference to choose with the software. I understood that the usual EEG reference selections are 1 electrode on top of the head (Cz), or the average of all connected electrodes... Someone could tell me what these two methods implies, how they differ and if one method is better than the other ?
> 
> Thank you in advance.
> 
> Best regards,
> Estelle Longin
> 
> 
> 
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Steven J. Luck, Ph.D.
Director, Center for Mind & Brain
Professor, Department of Psychology
University of California, Davis
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