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

[Tarik S Bel-Bahar]

Hello Isaiah, a few responses below, best wishes.

pop_interp should create a new channel that is interpolated. "add ref
channel back to data" should just not throw away the channel or channels
used to rereference to. I don't think that "add ref channel back to data"
recalculates anything, but one can check the function code.

When interpolating and referencing another data set that has more channels,
I think it matters not whose data it is. It's only using the channel
information from that dataset.

Regarding your question 2, I'm not sure but would say you could try
removing the non-data Cz if eeglab does not give you an error message..
When you say there 68 values in chanlocs I assume you mean 64 data
channels, one Cz, and 3 fiducials.

Try doing the procedure by exporting 64 channels without Cz from Netstaton,
and then going through your steps. Use the 64+Cz file only as the "second
file" you mention in point number 3.

If you haven't please check out an earlier note on this message thread with
a matlab codelet that may be useful to you. In that code I think it seemed
one solution was to just call cz chan 65 or something like that.

You may also directly edit the chan locations file that is loaded in eeglab.

Last, make sure that you've loaded your own correct EGI chan locations
file, don't rely on eeglab to pick the right one by itself.

If you can replicate an issue or are blocked, please consider reporting it
to eeglablist bugzilla. Thanks for sharing any solutions with other EGI
users on the list.






On Mon, Apr 18, 2016 at 4:32 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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