[Eeglablist] Should Average Reference Include Eye Channels?

[Matthew Stief]

Thanks to all the responses so far!

I am using a 128 channel BioSemi ActiveTwo system, so the eye channels
are not bipolar.  I imported with a reference to the linked mastoids,
and would like to rereference to the average.  My worry was the one
raised by Simon-Shlomo below, which is whether or not the extra
artifactual activity in the eye channels would contaminate the other
channels.

This possibility, I gather, is balanced against the goal of having as
many electrodes covering the head as completely as possible to match
the assumption of average referencing as closely as possible, as Robin
mentioned.

Makoto, what is your opinion on these two issues?  I am planning on
running ICA, not for artifact detection but to isolate the P1, and was
planning on including the eye channels to better separate out those
those artifactual sources.  And just to be sure I understand you, you
are saying that if I rereference to the average of only the 128 scalp
electrodes, and then run ICA on all 132 electrodes, that ICA will
average reference the data to all 132 electrodes again?  I believe I
remember reading that referencing after epoching and baseline removal
is erroneous, so how is that possible?



On Thu, Feb 9, 2012 at 5:15 PM, Simon-Shlomo Poil
<poil.simonshlomo at gmail.com> wrote:
> Dear Matthew,
>
> I would recommend you not to include your eye channels in your average
> reference.  If you still have eye-blinks in these channels, they will
> just contaminate your other channels.
>
> (If you already removed your eye-blinks using ICA, it's probably ok to
> include them in the average reference.)
>
> -Simon-Shlomo Poil
>
>
> 2012/2/9 Matthew Stief <ms2272 at cornell.edu>:
>> Greetings!
>>
>> I am using a 128 channel BioSemi active system, and am importing my
>> files using the average mastoids as the reference.  I would like to
>> rereference to the average, but am unsure if I should use my four eye
>> electrodes.  I read in the archives that this shouldn't be done for
>> eye electrodes that do not have the same reference as the scalp
>> electrodes, but given that in this case they do is there any reason
>> not to do it?
>>
>> --
>> _________________________________________________________________
>> Matthew Stief
>> Human Development | Sex & Gender Lab | Cornell University
>> http://www.human.cornell.edu/HD/sexgender
>>
>>
>> Heterosexuality isn't normal, it's just common.
>> -Dorothy Parker
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>
>
> --
> Simon-Shlomo Poil
>
> Webpage: http://www.poil.dk/s/ and http://www.nbtwiki.net



-- 
_________________________________________________________________
Matthew Stief
Human Development | Sex & Gender Lab | Cornell University
http://www.human.cornell.edu/HD/sexgender


Heterosexuality isn't normal, it's just common.
-Dorothy Parker