Survey of Eye Tracking Techniques

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• Survey of Eye Tracking Techniques

PSYC 736 Spring 2006
Observable(Quantifiable) Eye Movements
Covert Information Processing
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• Introduction

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Acuity as a function of retinal location
Visual acuity drops off rapidly from the fovea
to the visual periphery as shown in this figure.
The best visual acuity is found in a
parafoveal area of 1-4 degrees from the fovea.
(adapted from Schmidt and Connolly, 1966)
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Courtesy of Stuart Anstis

• Photographic Simulation of
• Variable Retinal Spatial Resolution

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To process visual detail we must move our eye
balls so that we aim them in such a way that we
get the greatest resolution which is in the
fovea.
Anatomy of the human eye ball The muscles of the
eye, 1) superior rectus muscle, 2) inferior
rectus muscle, 3) lateral rectus muscle (lateral
rectus muscle lies symmetrically opposite), 4)
superior oblique muscle, 5) inferior oblique
muscle. (adapted from Yarbus, Eye movements and
vision, page 13)
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Reproduction of Levitans picture The Flood
shown to five observers for free examination, and
graph of the distribution of 2000 drifts in
accordance with their duration.
Abscissas-duration of the drifts ordinate-number
of drifts of approximately equal duration.
(adapted from Yarbus, Eye Movements, page 111)

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• Usually an eye fixation takes about 0.4 seconds
  (2.5 fixations/second)
• 602.5150 eye fixations/minute
• 601509000 eye fixations/hour
• 169000144000 eye fixations/day
• 144000 is an average number of eye fixations per
  day or a number of visual details processed per
  day
• Usually the brain processes all visual
  information taken during a fixation and initiates
  the execution of the any action, if any execution
  is required. If too much information or
  uncertainty is present, then another fixation is
  necessary.

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Eye Tracking Techniques

• Electrooculography (EOG)
• Contact Lens Techniques a. Scleral coil b.
  Mirror reflector
• Limbus Tracker
• Video-based Pupil/Corneal Reflection
• Dual Purkinje Image
• Subjective Video Analysis

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• Electrooculogram (EOG)

• Exploits dipole nature of eyeball (retina is
  negative re cornea)
• DC amplification (hence, drift problems)
• Two pairs of electrodes (horz v. vertical) plus
  ground references
• High temporal resolution (continuous)
• Poor spatial resolution and/or accuracy

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• Scleral Search Coil

-based on current flow through induction
loop -good temporal resolution (pulsed 1000
Hz) -supreme spatial resolution (lt 10
arcsec) -uncomfortable -easily accommodates
animal research
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• Scleral Mirror(Yarbus, 1967)

-suction cup mounted mirror reflects optical
reference beam -significant inertial mass -goods
temporal resolution -moderate spatial accuracy (1
deg) -extremely uncomfortable -requires
anesthesia -very brief sampling epochs only -head
immobilization required
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• Limbus Tracker

-based upon differential reflectance of sclera
and iris -high temporal resolution (lt 1000
Hz) -poor spatial accuracy -very limited
operating range 10 deg horizontal
EMs only
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• Corneal Reflection Technique(s)

-based on real-time image processing to
recognize and localize pupil and corneal
reflection -IR illuminator required -temporal
resolution depends upon eye camera frame rate
(60, 120, 240, 500 Hz) -moderate spatial accuracy
(lt 1 deg) -bright pupil (robust) versus dark
pupil (daylight) -head mounted vs. remote optics
Bright Pupil (Coaxial IR Illumination)
Dark Pupil
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• ASL Model 501(USD Vision Lab)

• - head-mounted optics
• bright pupil
• single corneal reflection
• visor-based coordinates
• world-coordinates available
• via optional head tracker and
• stationary scene camera
• - 60 Hz (240 Hz optional available)

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Corneal Reflections/Calibration
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Measuring DriverEye Movement Behavior
ASL Model ETS-PC(USD Vision Lab) -dark pupil
(day/night operation) -remote optics with smart
pan/tilt -dual corneal reflections (CR) -wide
field-of-view (60-75 deg) -world coordinates
(stationary scene camera) -60 Hz (high speed
option not available)
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USDInstrumented Research Vehicle
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ASL ETS-PCDriver Eye Tracking System
Infrared Illuminators (source of corneal
reflections)
Hidden Eye Tracker Optics
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Hidden Eye Tracker Optics
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Eye Tracker Operator(Rear Seat)
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Test Driver
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(No Transcript)
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Corneal Reflections/Calibration
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Some ExamplesofDriver Eye Movement Records
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SD HWY 50 West
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Main Street - Vermillion
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Cherry StreetSlow Moving Vehicle
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• Saccade Detection Latency Comparison
• ASL 501 versus Limbus Tracker(Gaze Contingent
  Eye Tracking)

Courtesy of Jochen Triesch, UCSD
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• Head-mounted Display (VR)

Courtesy of Jochen Triesch, UCSD
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• Dual Purkinje Eye Tracker

-based upon alignment (parallax) of Purkinje
images I and IV -excellent spatial resolution
and accuracy (lt 1 minarc) -uncomfortable
(requires bite bar) -Gold standard for human
lab psychophysical studies
Courtesy of Jochen Triesch, UCSD
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• Subjective Localization of Gaze
• (Frame-by-frame Video Analysis)

Accuracy Map Subjective Estimation of In-Vehicle
Gaze Position (Camera position 65-deg from L.O.S)
Schieber, et al., 1997
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Older Driver Performance MetricsInternet-in-the-C
ar (Driver Distraction)
video clip next screen
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Older Driver Performance MetricsInternet-in-the-C
ar (Driver Distraction)
(click to start video clip)