advantage of "linked ears" reference vs single reference?
Hi,
I am looking to understand the advantages of 2 linked ears reference over just 1.
Isn't one enough to help cancel the EMF for the electrodes on the head anywhere? Or is there a phase difference in the EMF activity with only a short distance, from left to right part of the head?
Comments
Many legacy neurofeedback systems use "linked ears" for reference. This is where the left and right ear lobe electrodes are electrically connected via a linking cable, directly shorted so that the reference lead connects to both ears. This is widely used in QEEG recordings, so has become a standard in that field.
On the other hand in research settings with an electrode cap, it is common to use just a centrally located (on the midline) single reference. Many caps (such as those sold in the Shop), have this ability. For example they may place the reference at POz or CPz.
In any reference scheme it is possible to 're-reference' via straightforward math operations.
https://www.google.com/search?q=re-reference+eeg
'Canceling' EMF via injection of an anti-mains 'common-mode' low level signal, is a function performed by the 'Bias' or 'Ground' lead on some amps. This is why this lead is best also placed on the midline. For example with Electro-caps (used in QEEG), this is placed at AFz.
William