[Eeglablist] EEG reference BioSemi system

[Andrew Hill]

Hi Estelle,

It really depends on the questions you are asking of your EEG.

I'd suggest just using any single channel to import BioSemi to avoid losing signal info (I use Pz since it's close to the CMS-DRL location of the BioSemi system), and then re-reference in EEGLAB to whatever you want after cleaning the data.

The reference should probably be chosen to mimic similar research, so you can compare your results to other papers - especially important in ERP research.

I'd suggest either using an average mastoid / average ear reference or a whole-head reference.  Most ERP seems to use one or the other, and they produce similar scalp distributions (although avg head is reduced in amplitude compared to avg ears).

If you aren't doing ERP, it doesn't matter as much, but you will prob still have a rationale based on existing research you want to ultimately compare your results to.

Note that BDF files have a large DC offset, so you should either use BioSemi supplied "Converter" to BDF->EDF (I use the default setting of 0.16 hz highpass filter) or filter the data once in EEGLAB, e.g highpass above 1 hz or so.  Filtering at 1hz is pretty bad for ERPs - smears them - but should be ok for other EEG analyses.

Best,
andrew


On Jan 10, 2012, at 3:24 AM, Estelle Longin wrote:

> 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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