[Eeglablist] Average re-reference

[Scott Makeig]

Chiara -  Any (valid) re-referencing of EEG data is equally valid (e.g.,
re-referencing to any channel combination, including to the average of all
channels ('average reference'). None is more correct than any other. Any
scalp channel represents the sum and difference of activity across much of
cortex. This is why we focus ICA component measures, which are reference
free (except for the IC scalp maps for this we typically use average
reference).

However, to compare scalp values *across* studies, the measures being
compared should use the same reference.

Scott Makeig

On Tue, Oct 20, 2020 at 4:15 PM Chiara Terzo <Chiara.Terzo at iit.it> wrote:

> Dear all,
>
>
> I estimated evoked-potentials of an EEG data set collected with 32
> channels. With the reference to the right mastoid I get a specific pattern
> of evoked that are consistent with the previous literature (i.e. positive
> late potentials around 400ms). However, if before doing ICA I re-reference
> my data to the common average (as it's highly recommended), I get a
> different pattern, such as late potentials  being negative. Which one of
> the two should then be reliable? Is it necessary to re-reference to average
> before doing ICA? And how much not doing so would bias my results?
>
>
> Thank you for your help,
>
>
> Chiara
>
>
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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation, University of
California San Diego, La Jolla CA 92093-0559, http://sccn.ucsd.edu/~scott