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

Evans, Ian D. ievans at une.edu.au
Sun Sep 5 07:15:41 PDT 2010

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 
Sent: Sunday, September 05, 2010 8:08 PM
To: Evans, Ian D. 
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?


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
Phone: +44 (0131) 6503063
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