[Eeglablist] Re-referrence to average and add Cz back

[Isaiah Innis]

---------- Mensaje reenviado ----------
From: Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
To: Fang-Yu Chang <hardheard101 at gmail.com>, EEGLAB List <
eeglablist at sccn.ucsd.edu>
Cc:
Date: Wed, 13 Apr 2016 12:25:54 -0700
Subject: Re: [Eeglablist] Re-referrence to average and add Cz back
Dear Fang-Yu,

> If I would like to add Cz back with computing average, should I operate "
're-reference'-> 'Compute average reference' with 'add current reference
channel back to the data' ?"

Compute average reference first and then interpolate Cz next.

> I would like to ask more question. You mentioned one(any) channel need to
be discarded after computing average. How do I discard one channel? I
operated " 'Edit' -> 'Channel locations' -> 'delete channel' " by EEGLAB,
but it didn't work. I'm not sure it is right to operate like this.

Yes this is confusing. Sorry for that. What you need to do is to 'Select
data' and not channel editing. Select a channel to discard from the list,
check the box to perform rejection for the selected (otherwise it'll leave
the selected).

Makoto

On Tue, Apr 12, 2016 at 11:44 PM, Fang-Yu Chang <hardheard101 at gmail.com>
 wrote:

> Dear Makoto,
>
> Thanks for your reply. I think I just confused with adding Cz back and
> interpolating Cz, and Cz dose exist in my dataset.
> If I would like to add Cz back with computing average, should I operate "
> 're-reference'-> 'Compute average reference' with 'add current reference
> channel back to the data' ?"
>
> I would like to ask more question. You mentioned one(any) channel need to
> be discarded after computing average. How do I discard one channel? I
> operated " 'Edit' -> 'Channel locations' -> 'delete channel' " by EEGLAB,
> but it didn't work. I'm not sure it is right to operate like this.
> Thanks for your help in  advanced.
>
> Sincerely,
> Fang-Yu Chang
>


Hello EEGLab list:

I still have some confusion regarding Re-referrencing to average and adding
Cz back for an EGI system.

1) There seem to be two options - interpolation using pop_interp and the
checkbox to "add ref channel back to data" using pop_reref. They produce
different results when used:

https://onedrive.live.com/redir?resid=A1398B0A4C8F85DE!2206&authkey=!AMJUTORsc9y3ao4&v=3&ithint=photo%2cpng

It seems from the discussion here that interpolation after rereferencing is
the correct option - I assume because these functions differ in how they
calculate Cz?

2) After interpolation I receive the following message: "Warning: some
channels have the same label." Checking the chanlocs struct there are now
two Cz entries, one marked as a data channel and one not. Is this a
problem? Should I delete the non - data Cz? When importing channel
locations for our 64 channel system, there are 68 values in chanlocs; after
interpolation there are 69.


3) When interpolating Cz, do I need to have a dataset with Cz from the same
subject or can it be any dataset with Cz? Do I have to manually edit
pop_chanedit to get Cz in a dataset?  I have been using datasets from the
same subject, but this issue has made me question that.



Thank you in advance,
-- 
Isaiah Innis
Indiana University '13
EEG Technician, IUB IRF
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