[Eeglablist] Saccades from EOG data

[Scott Makeig]

Scott -

In simple cases (e.g., eye movements from screen center to screen radius in
all directions) ICA will typically find 2 component processes coding
orthogonal directions of movement (i.e., forming an orthogonal basis for a
two-dimensional space of movements). These need not be horizontal and
vertical directions however (though they are in situations where eve
movements are predominantly in these directions). In more complex cases (eye
movements during global image search), the decomposition of eye movement EOG
by ICA might be more complex. The general procedure would be to find the
subspace of such components (by their scalp maps and time courses), then
compute a best-fitting mapping of this IC subspace (values of all the
subspace ICs at a given instant) with known eye movement directions (e.g.,
results of an initial calibration procedure performed during the experiment,
or known/assumed eye movement directions time locked to particular exp.
events). Most simply, this could use multi-dimensional linear regression.

For max possible accruacy, more extensive calibration data and nonlinear
regression methods might be needed -- IF the subject's head position re the
screen is fixed (e.g. by a chinrest). If not, then the position and
orientation of the head must also be tracked and this info incorporated into
the movement direction algorithm. We are now doing this for mobile head-worn
eye tracking, but don't have the method completed yet.

Scott Makeig

On Mon, Jun 27, 2011 at 3:15 PM, Scott Munro <phaddie at gmail.com> wrote:

> Hello,
>   We have a set of EOG data extracted from a CTF MEG scanner.  We are
> hoping to isolate the horizontal direction of saccades and their timing.  I
> am very new to EEGlab and to EEG type data in general.  I am actually not
> sure even where to begin.  I have found some criteria in literature but not
> sure how to implement it.  I also suspect I may need to use ICA, but as of
> yet I have not been able to determine how to achieve our goal using ICA.
>
>   Any help or guidance in the right direction would be helpful.
>
>     Scott Munro
>     Department of Cognitive Science
>     York University
>
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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation & Adj. Prof. of
Neurosciences, University of California San Diego, La Jolla CA 92093-0559,
http://sccn.ucsd.edu/~scott
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