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

[Makoto Miyakoshi]

Dear Isaiah,

> 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?

I thought whichever works is fine...until I clicked the link. Wow. Why are
they so different? Are you sure that you rejected all bad channels before
the process?

> 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?

I believe you can't have two channels with the same name.

> Should I delete the non - data Cz?

Yes, why not.

> 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?

I thought that's easier if you are using EEGLAB. Have one 'template
subject' who has all the channels, and always refer to the one to
interpolate whatever is 'missing' compared with it.

> Do I have to manually edit pop_chanedit to get Cz in a dataset?

Whichever more convenient for you (and works) is fine.

Makoto



On Mon, Apr 18, 2016 at 1:32 PM, Isaiah Innis <isainnis at umail.iu.edu> wrote:

> ---------- 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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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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