[Eeglablist] Question on Reference Channels to use when loading EEG data in EEGLab

[Tarik S Bel-Bahar]

Hello Jessica, hoping the brief suggestions below help, all the best!





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If you have not had a chance to, please review the online eeglab tutorial
and info for useful details. A google search with your question can also
bring up some answers that you find useful, from eeglablist, and from
elsewhere. If you have not, try opening one of the sample eeglab files, and
review the channel locations information via the GUI and by looking at the
correct fields of the EEG structure in matlab.

0. In brief, there are usually numbers on the electrodes. Also there are
usually electrode layout files that contain the Number of each channel,
most likely including the nose channel you were asking about, unless it was
added by your team and that channel was not already a part of the EEG net
used for collection, ie an auxiliary channel).
1. try to get eeglab to just load all data for all channels first, and then
work to apply correct labels to the channels, once the data is in eeglab.
You may apply the correct labels via the gui (Edit channel locations), or
manually. it can be a little tricky, but works well for most major eeg
electrode layouts.

2. Once you've loaded in a channel location file that eeglab accepts, then
you should be able to edit channel locations via the eeglab gui, and view
them

3. For electrode numbers, you need to get the layout, labels, and channel
numbers, which can usually all be found in a "channel locations" file" for
the system on whcih the data was collected. See eeglab's channel location
list, findable via google if you search "eeglab channel locations". Also
consider contacting your data collector or system vendor for channel number
and position info. Eeglab is trying to guess which electrode layout to use,
I believe. Review the contents of the layout files and try to understand
how the channels are labelled before trying to get eeglab to read them.

4. Often, there are channels in an channel locations file that have unique
labels such as REF or Naz, etc.., and these usually are detected as the
reference channel(s) and as the fiducial points, and are not used as the
normal EEG channels.

5. For an average reference, you should be able to use the eeglab
rereferencing function available from the GUI menu, which allows
re-referencing to 1,2, or more electrodes. However once you re-reference
you have a choice of dropping or keeping the reference channels in the data.

7. For average reference, if you have 50+ channels, you should be able to
compute a valid average reference. For less channels, it depends on the
system, but the mastoid (ears) or noise reference might work. You should
most likely emulate referencing schemes published research done with that
same system.

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On Fri, Feb 13, 2015 at 3:18 PM, Jessica Satterwhite <jessksat at nmsu.edu>
wrote:

>  Hello,
>
>
>  I am new to EEGLab and am trying to load EEG data into EEGLab. When
> doing so, it asks you to include a reference channel before you are able to
> open the data or else it warns you that you will lose a significant amount
> of data. I have tried to research how to specify the common average
> reference but am still unsure of what to do. On one site, it said to simply
> choose an electrode on top of the head, or average the electrodes from
> either ear. We are not using electrodes on the ears but I thought I could
> perhaps use the electrode on the nose as a reference but am unsure how to
> put this in. How do you know what number that certain electrode is before
> you load the data? Also, is it better to average all electrodes to find the
> common average reference? If so, how does one go about doing this?
>
>
>  Thank you so much for any help you can give me.
>
>
>  Jessica Satterwhite
>
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