External Email - Use Caution
Dear Sylvain, Clemens, and Alex,
regarding the rationale:
- Say you recorded from 10 electrodes and referenced against another
electrode
- You thus have 11 electrodes, one of which contains a "zero" signal
(the reference)
- If you now apply the average reference, you are reducing the "rank" of
the data by one (see:
https://sccn.ucsd.edu/wiki/Linear_Representations_and_Basis_Vectors#EEG_Data_Reference_and_Re-referencing)
- Usually, the reference electrode is not included in the re-referenced
data ... so then you will have 10 electrodes and "full rank" data
- The problem arises by including the 11th electrode, because then you
would have rank deficient data.
- If you then re-reference the rank-deficient, average-re-referenced
data to mastoids again, you might run into problems (e.g., when trying
to run ICA).
I am not entirely sure about my reasoning, so another opinion would be
appreciated.
Best,
Stefan