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

Evans, Ian D. ievans at une.edu.au
Mon Sep 6 23:02:27 PDT 2010

I believe so - that is what I'm currently testing for. The current methods 
of removing eye movement artifacts involve regression analysis techniques 
which do filter out most of the artifactual potentials, leaving a largely 
pure EEG recording. It it my view (for now, at least) that ICA may be more 
accurate at detecting & thus filtering out EOG artifacts, leaving us with a 
much cleaner recording.

By measuring muscular activity around the eyes using the EOG electrodes 
real-time eye movement can be measured with a modicum of accuracy, at least 
enough accuracy to remove most artifacts. The challenge is measuring the 
effects on other electrodes, and this effect varies from person to person, 
and indeed recording to recording. This is why I start every EEG recording 
with a four-minute calibration task to measure & isolate types of eye 
movement (up, down, left, right, blink) so they can be corrected later.

But ultimately yes, with the right technique a simple subtraction of  EEG- 
associated EOG potentials from a recording is possible, and indeed 
encouraged. Current methods largely work well, but we can always do better.

Ian Evans
Cognitive & Affective Neuroscience
University of New England

From: "Bill Torch" <eyecomm at aol.com>
Sent: Tuesday, September 07, 2010 1:10 PM
To: "Evans, Ian D." <ievans at une.edu.au>
Subject: Re: [Eeglablist] Eye movement artifact in ICA - missing coordinates 
for EOG electrodes

> Ian, in response to your question, i have a question? If you had 
> quantitative EEG- associated EOG potentials that were directly tied to 
> actual real time eye movement coordinates, would you be able to subtract 
> these real time "artifactual" electrical potentials from the EEG
> get "pure" EEG?
> Dr. Bill Torch
> Medical Director, Neurodevelopmental & Neurodiagnostic  Ctr
> Sent from my iPhone
> On Sep 3, 2010, at 1:42 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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