[Eeglablist] Options for bad reference (mastoid) channels

[Makoto Miyakoshi]

Dear Becky,

> I believe the convention is to use the average of linked ears or mastoids
as the reference for optimal measurement of these components,

It depends on whether you want to use ICA to analyze your data in the
source-resolved EEG or not. If you do, re-reference does not affect the ICA
results. If you want to use channel EEG for the final analysis, I recommend
average referencing. If you need to choose 1 electrode, choose Cz or FCz
because that's another 'convention' I've seen so far (may not specific to
your task though). Cz and FCz are easy to interpolate.

Makoto

2013/9/18 Becky Prince <becky.prince at york.ac.uk>

> Dear EEGLAB list,
>
> I've run an ERP study on auditory temporal expectations in which I'm
> interested in the auditory N2b and P3b components.  I believe the
> convention is to use the average of linked ears or mastoids as the
> reference for optimal measurement of these components, but my mastoid
> channels are consistently noisy in all of my participants.  The mastoid
> channels have higher impedances (~15 KOhms) than the other sites, probably
> due to the fact that the caps we use have built in mastoid sites that don't
> fit close enough to the skin.
>
> I'm guessing it's a bad idea to re-reference to noisy channels, so I'm
> wondering what my options are.  Can anyone explain what they would do in
> this situation?  Are there any resources that explain the effects of
> re-referencing on specific components?  I'm wondering if I'll be able to
> see changes in N2b/P3b if I use another reference, e.g. average of all
> electrodes, and how the appearance of the components (sites/polarities)
> will be different from those typically reported with a linked ear or
> mastoid reference.
>
> Apologies for the fact that this isn't strictly an EEGLAB question - I'm
> hoping someone will still offer some advice!
>
> Thanks,
> Becky
> ____________________________________________
>
> Becky Gilbert (nee Prince)
> PhD Researcher
>
> Room A109
> Department of Psychology
> University of York
> Heslington, York, YO10 5DD, UK
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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