Survey of Eye
Tracking Techniques
PSYC 736 – Spring 2006
Observable
(Quantifiable)
Eye Movements
Covert
Information Processing
Introduction
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)
Courtesy of Stuart Anstis
Photographic Simulation of
Variable Retinal Spatial Resolution
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)
Reproduction of Levitan’s
picture “The Flood”
shown to five observers
for free examination, and
graph of the distribution
of 2000 drifts in
accordance with their
duration. Abscissasduration of the drifts;
ordinate-number of drifts
of approximately equal
duration. (adapted from
Yarbus, Eye Movements,
page 111)
Usually an eye fixation takes about 0.4 seconds (2.5 fixations/second)
60*2.5=150 eye fixations/minute
60*150=9000 eye fixations/hour
16*9000=144000 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.
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
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
Scleral Search Coil
-based on current flow through induction loop
-good temporal resolution (pulsed; 1000 Hz)
-supreme spatial resolution (< 10 arcsec)
-uncomfortable
-easily accommodates animal research
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
Limbus Tracker
-based upon differential reflectance of sclera and iris
-high temporal resolution (< 1000 Hz)
-poor spatial accuracy
-very limited operating range
10 deg
horizontal EMs only
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 (< 1 deg)
-bright pupil (robust) versus dark pupil (daylight)
-head mounted vs. remote optics
Bright Pupil
(Coaxial IR Illumination)
Dark Pupil
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)
Corneal Reflections/Calibration
Measuring Driver
Eye 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)
USD
Instrumented
Research Vehicle
ASL ETS-PC
Driver Eye Tracking System
Infrared Illuminators
(source of corneal reflections)
Hidden Eye Tracker Optics
Hidden Eye Tracker Optics
Eye Tracker Operator
(Rear Seat)
Test Driver
Corneal Reflections/Calibration
Some Examples
of
Driver Eye Movement Records
SD HWY 50 West
Main Street - Vermillion
Cherry Street
Slow Moving Vehicle
Saccade Detection Latency Comparison
ASL 501 versus Limbus Tracker
(Gaze Contingent Eye Tracking)
Courtesy of Jochen Triesch, UCSD
Head-mounted Display (VR)
Courtesy of Jochen Triesch, UCSD
Dual Purkinje Eye Tracker
-based upon alignment (parallax)
of Purkinje images I and IV
-excellent spatial resolution
and accuracy (< 1 minarc)
-uncomfortable (requires bite bar)
-”Gold standard” for human
lab psychophysical studies
Courtesy of Jochen Triesch, UCSD
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
Older Driver Performance Metrics
Internet-in-the-Car (Driver Distraction)
video clip next screen
Older Driver Performance Metrics
Internet-in-the-Car (Driver Distraction)
(click to start video clip)