Rereferencing for somatosensory ERPs

[francis24]

Dear all,
I am currently looking into data from a somatosensory experiment (participants received vibrations on the tip of their middle finger) and I am trying to find the best parameters for seeing somatosensory ERPs. I am using a 64 Channel Biosemi & ActiView recording system, preprocessing is done in FieldTrip.

I was advised by colleagues to not rereference at all but then I read about on the Biosemi Website :'When no reference is selected in software, the signals are displayed with respect to the CMS electrode. This mode does not provide the full CMRR, and should only be use as a quick check of the electrodes. Only after a reference is selected, the full 80 dB CMRR is achieved.'
Does this mean that it would be necessary for me to rereference in Fieldtrip? If so would you recommend referencing to average of all 64 electrodes or another method? Unfortunately we had no mastoid or ear electrode in the EEG setup.


Many thanks
Francis

[Coen]

Your colleagues are wrong, it is always necessary to reference the data before further analysis.

You could consider using the average from T7 and T8 as an alternative for your missing linked mastoid.

Best regards, Coen (BioSemi)

[francis24]

Many thanks for the clarification and advice