[Eeglablist] Data Collection - Average Reference

Arnaud Delorme arno at ucsd.edu
Sat May 18 09:21:24 PDT 2013


Dear Balaji,

I agree with Roy about re-referecing. Re-referencing is a benign reversible mathematical operation. There is no reason why you should not be able to do it.
I have also used ANT in the past and have processed data with linked mastoid. However, I prefer to use average reference now, based on some reports that shows its superiority in some applications (http://www.ncbi.nlm.nih.gov/pubmed/20547470).

Arno

On 16 May 2013, at 02:16, Roy Cox wrote:

> Hi,
> 
> I use the ANT system. The amplifier itself uses, as you say, an average reference natively. That's also the montage I use for recording. For online viewing purposes I do have a (viewing) montage that uses linked M1/M2 as a reference. But this does not affect the way your data is stored.
> 
> After converting data data into an eeglab structure, I always re-reference to linked mastoids. Something like EEGreref=pop_reref(EEG,[13 19],'keepref', 'off'); Assuming chans 13 and 19 are your mastoids.
> 
> I've never heard of not re-referencing from average reference before. That would mean you're forever stuck with the average reference used for recording. So I wouldn't buy that.
> 
> The reference scheme does affect your ERPs: with an average ref, all signals must sum to zero. So a large frontal positive component will usually be matched by posterior negative deflections (see what happens with eye blinks for example). Using linked mastoids as the reference, eye blink activity will remain frontal. So, in case you want to compare your results to things in the literature, I would definitely make sure you have the same referencing scheme.
> 
> Roy 
> 
> 
> On Wed, May 15, 2013 at 12:33 PM, Becky Prince <becky.prince at york.ac.uk> wrote:
> Dear Balaji,
> 
> I'm also an ANT Neuro EEG system user, and I've actually been wondering the same thing, so thanks for asking!  Our data is recorded with average reference by default, and I don't re-reference the data after collection.  I'm not sure if anyone else does things this way, and under what circumstances the data should be re-referenced after collection.  Also, I've been wondering if my averaged ERP waveforms look different from those typically reported in the literature because of differences in the way that ERPs are referenced (e.g. linked ears or mastoids rather than average).  Hopefully someone who knows more about this can enlighten us both!
> 
> Best,
> Becky
> 
> PhD candidate
> Department of Psychology
> University of York
> York, England
> 
> On 13 May 2013 18:53, Lakshmanan, Balaji <lakshmanan at kennedykrieger.org> wrote:
> Dear EEGLAB users,
> 
>  
> 
> We collect data using ANT EEG system which by default uses average reference during data collection.
> 
> We've been collecting this way for very long and analyze our data using the same. Sometimes we do change the reference offline to compare our results with various reference options.
> 
> Recently we were told by one of the researchers that it is not correct to change the reference (for e.g. to linked ears), if the data was originally recorded using average ref. However looks like vice-versa is possible.
> 
>  
> 
> I always thought re referencing offline is never an issue no matter what your recording montage/reference is. Any explanation/thoughts on this issue is appreciated.
> 
>  
> 
> Also, I would like to know what ref. ANT users generally use to record EEGs and for their analyses?
> 
>  
> 
> Thanks,
> 
> Balaji
> 
>  
> 
> 
> 
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> -- 
> Roy Cox, M.Sc. | Brain & Cognition Group | Department of Psychology | University of Amsterdam | Weesperplein 4 | 1018 XA Amsterdam | the Netherlands | room 3.21 | phone: +31 20 525 6847 | email: r.cox at uva.nl
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