[Eeglablist] when to re-reference

[Stephen Politzer-Ahles]

Hello Bin,

If you have bad channels that need to be interpolated, this must be done
before average referencing (see previous messages on the list about this
issue).
I also suspect that referencing may need to be done before artifact
rejection, depending on how you do artifact rejection, because some of the
methods will be affected by your choice of reference. For example, if you
reject based on extreme values (and apply this to all channels), you can
imagine a situation where a given channel might not exceed the value if the
reference is e.g. Cz but might change to exceed the value once the
reference is changed to e.g. mastoids. Ultimately, whether or not this is
an issue will depend on how you plan on doing artifact rejections, and
properties of your system (e.g., whether you have bipolar EOGs that use
their own reference separate from the rest of the electrodes).

There may also be other issues that I haven't thought of here, others on
the list may be able to clarify more.

Best,
Steve



Stephen Politzer-Ahles
New York University, Abu Dhabi
Neuroscience of Language Lab
http://www.nyu.edu/projects/politzer-ahles/

On Sun, Nov 30, 2014 at 6:48 PM, Bin Wang <binwang87828 at gmail.com> wrote:

> Dear all,
>
> One simple question: I would like to try several different reference
> selections (i.e. average or mastoid), hopefully, I can find a relatively
> better one. My question is if the re-reference step must be done before
> epoch the data and artefact removal. Because I want to do all of
> preprocessing steps and artefact removal, and then apply several different
> re-reference selections, by this way I don’t need to do all of
> preprocessing steps again. Does it sound fine? Is there any other artefacts
> or problems that will be induced by the re-reference of last step.
>
> I am looking forward your any advices
>
> Thank you in advance,
>
> Bin
>
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> Cognitive Neuroscience
> Institute of Neuroscience and Medicine (INM-3)
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