[Eeglablist] Data Collection - Average Reference

[Roy Cox]

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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