Impact of reference electrode for import on data ?

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bert
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Joined: Mon Sep 10, 2018 9:26 am

Impact of reference electrode for import on data ?

Post by bert » Thu Nov 01, 2018 11:15 am

When importing BDF file into EEGLAB, Biosemi users are prompted to select a reference electrode. Usually I use here a midline electrode (Cz or POz in my case). However, Cz and POz are also critical electrodes in the regions of interest in my experiments.

My question is whether the choice of reference electrode(s) for data import influences (in any manner) the quality of the signal measured at those electrodes ? Or does it have no influence at all on the values for that electrode.
When I re-reference to, e.g., the average after ICA, does that mean that the values for the chosen reference while importing have been substituted with the average values, or does it mean that the orginal values have been linearly adapted to the average, without further loss of data quality ?

Thanks for your comments/considerations on this question,

Bert

Coen
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Re: Impact of reference electrode for import on data ?

Post by Coen » Fri Nov 02, 2018 12:49 pm

A voltage is a difference in potential. So, the choice of reference does of course affect the eventual EEG voltages. The choice during import does not affect later alternative choices of the reference.

Best regards, Coen (BioSemi)

bert
Posts: 2
Joined: Mon Sep 10, 2018 9:26 am

Re: Impact of reference electrode for import on data ?

Post by bert » Sun Nov 04, 2018 7:57 pm

Coen

Thank you for your response. I had one extra question.

With "non-biosemi" devices, a reference is chosen before eeg-recording. Then, it is usually advised not to choose an electrode that is an electrode of interest for your type of experiment, e.g., Cz in a language experiment.

Do Biosemi-users have to take into account the same advice while choosing an electrode for import, or does it not matter ?

Thanks for your response and consideration of this question,

Bert

Coen
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Re: Impact of reference electrode for import on data ?

Post by Coen » Mon Nov 05, 2018 3:13 pm

It does not matter. A reference far away generates high Common Mode voltages, a reference close to the area of interest generates small signal amplitudes. Re-referencing cancels these effects.

Best regards, Coen (BioSemi)

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