[Eeglablist] Eye movement artifact in ICA - missing coordinates for EOG electrodes

Baris Demiral demiral.007 at googlemail.com
Thu Sep 9 10:58:33 PDT 2010


Well, I acknowledge that the labels are arbitrary at this point, but I
propose to the eeglab community that we use the EOG labels as follows:

Horizontal:
H1:      EOG on the Left Temple (H indicating horizontal)
H2:      EOG on the Right Temple

Vertical:
VA1:      EOG Above the Left Eye (V indicating Vertical)
VB1:      EOG Below the Left Eye

VA2 and VB2 respectively on the right eye.

Mastoids (already agreed):
M1: Mastoid Left
M2: Mastoid Right


At least if I can have the coordinates of these positions (which some of you
already agreed upon) it will be fabulous. And I think I would only include
H1, H2, and VA1 and VA2  EOGs in my IC computations, because the VB1 and VB2
are generally prone to the local mouth, cheek and lip movements and may not
be contaminating the EEGs that much.

Regarding to your findings, Ian, I think adding EOG channels will lead to
the fallowing: Increase the number electrodes --> increase the number of of
ICs --> which will naturally increase the number of artefact containing ICs
--> this will bias some of the the artefactual ICs to shift towards the face
or anterior regions. It looks like adding up EOGs in ICA based
corrections/rejections is better to diagnose and differentiate very anterior
components such as ELAN or LAN form the eye movement related artifects. For
instance if you see an IC on F7 it is possible that it is a left anterior
negativity but not an artefact. I recently used ADJUST, and I am wondering
whether anyone using or developing ADJUST can help us to understand how
ADJUST will behave in this case. I am very much interested in artefact
correction.

Related to Scott's point: We use bipolar EOG electrodes in a BioSemi system
and when we import the file into eeglab we use one of the mastoid electrodes
as a reference. As far as I understand, bipolar electrodes referenced to the
same electrode as the other EEG electrodes will not cause any problem for
ICA based rejections in this case. Is this correct?

Thanks,

Baris



On Sun, Sep 5, 2010 at 3:15 PM, Evans, Ian D. <ievans at une.edu.au> wrote:

>  Shall endeavor to find out this week, if there's time amongst the
> residential schools. But from what I can discern the EOG electrodes do seem
> to make a difference - when I ran an ICA on the eye calibration task used to
> measure artifact without any EOG electrodes in the mix, around 40 of the 68
> components highlighted the F8 region as a strong source, and this in a task
> purely involving eye movement, no other processing involved other than
> possibly recognizing the shapes used to indicate where the subject should
> look. Tried running it again but included some estimated positions of
> EOG electrodes at the front, and there were still 40+ components all
> indicating activity at the frontal lobe, but now the activity was around the
> face instead of F8. If nothing else, the EOG information should assist ICA
> by isolating changes in multiple electrodes with correlate with the EOG data
> and rendering it completely independent from the underlying actual data.
>
> As for labels, well I couldn't find any consistent EOG labeling systems for
> MATLAB, so why not start gathering labels? Let me know what labels you use
> for the eye channels and I can build the .loc file - David Groppe (many
> thanks again!) sent me a set of coordinates for the ocular electrodes, but
> there is no problem with having multiple names for the same set of
> coordinates - EEGLab detects what we're using anyway. Worth a shot.
>
>
> Ian Evans
> Cognitive and Affective Neuroscience
> University of New England.
> ievans at une.edu.au
>
>  *From:* Baris Demiral <demiral.007 at googlemail.com>
> *Sent:* Sunday, September 05, 2010 8:08 PM
> *To:* Evans, Ian D. <ievans at une.edu.au>
> *Cc:* eeglablist at sccn.ucsd.edu
> *Subject:* Re: [Eeglablist] Eye movement artifact in ICA - missing
> coordinates for EOG electrodes
>
> Hi Ian,
>
> I also made a similar query few months ago. I use 64 electrode 10-20 system
> plus 4 EOGs. I asked whether there are specific labels for such EOG
> electrodes in the standard-10-5-Cap385.sfp so that I can map these
> electrodes on the fly. Are there labels for those, or can we decide and add
> those labels and coordinates as a community together?
>
> Actually, I find something more important: How much really does this
> influence ICA related artifact detection and correction? Is there a huge
> change when you include horizontal and vertical EOGs in the ICA based ERP
> calculations? Are there others over there who compared  ICA based
> computations with and without including the EOG electrodes?
>
> Baris
>
> On Fri, Sep 3, 2010 at 7:42 AM, Evans, Ian D. <ievans at une.edu.au> wrote:
>
>> Greetings all! I'm trying to isolate eye movement artifact with ICA in an
>> attempt to make EOG correction more accurate and hopefully remove less of
>> the genuine underlying data that regression methods might otherwise
>> remove,
>> however I am having trouble tracking down a satisfactory scalp map that
>> includes co-ordinates (Cartesian, 2D polar, 3D cylindrical) for the EOG
>> electrodes on the face. Neither Neuroscan nor any setup or .loc files in
>> EEGLab seem to provide these details, and all attempts to isolate eye
>> movement in ICA without the location of the eye movement electrodes have
>> been met with mocking laughter.
>>
>> The recordings have already been made on a 64-channel cap with six EOG
>> electrodes (one above and below each eye, another beside each eye for
>> horizontal eye movement) using the traditional 10-20 system. All
>> co-ordinates for the scalp are already at hand, just the facial electrodes
>> are needed. If anyone can make such a coordinate map available it would be
>> most helpful, thank you kindly!
>>
>> Ian Evans
>> Cognitive and Affective Neuroscience
>> University of New England.
>>
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>
>
>
> --
> SB Demiral, PhD.
> Department of Psychology
> 7 George Square
> The University of Edinburgh
> Edinburgh, EH8 9JZ
> UK
> Phone: +44 (0131) 6503063
>



-- 
SB Demiral, PhD.
Department of Psychology
7 George Square
The University of Edinburgh
Edinburgh, EH8 9JZ
UK
Phone: +44 (0131) 6503063
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