1. Survey of Eye Tracking Techniques
PSYC 736 – Spring 2006
Observable (Quantifiable)
Eye Movements
Covert
Information Processing

2. Introduction

3. 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)

4. Photographic Simulation of Variable Retinal Spatial Resolution
Courtesy of Stuart Anstis
Photographic Simulation of
Variable Retinal Spatial Resolution

5. Anatomy of the human eye ball
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)

6. 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. Abscissas-duration of the drifts; ordinate-number of drifts of approximately equal duration. (adapted from Yarbus, Eye Movements, page 111)

7. 60*2.5=150 eye fixations/minute 60*150=9000 eye fixations/hour
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= eye fixations/day
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.

8. 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

9. 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

10. 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

11. 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

12. Limbus Tracker -based upon differential reflectance of sclera and iris
-high temporal resolution (< 1000 Hz)
-poor spatial accuracy
-very limited operating range deg
horizontal EMs only

13. 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

14. 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)

15. Corneal Reflections/Calibration

16. 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)

17. USD Instrumented Research Vehicle

18. ASL ETS-PC Driver Eye Tracking System
Infrared Illuminators
(source of corneal reflections)
Hidden Eye Tracker Optics

19. Hidden Eye Tracker Optics

20. Eye Tracker Operator (Rear Seat)

21. Test Driver

23. Corneal Reflections/Calibration

24. Some Examples of Driver Eye Movement Records

25. SD HWY 50 West

26. Main Street - Vermillion

27. Cherry Street Slow Moving Vehicle

28. Saccade Detection Latency Comparison
ASL 501 versus Limbus Tracker (Gaze Contingent Eye Tracking)
Courtesy of Jochen Triesch, UCSD

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

30. 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

31. 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

32. Older Driver Performance Metrics Internet-in-the-Car (Driver Distraction)
video clip next screen

33. Older Driver Performance Metrics Internet-in-the-Car (Driver Distraction)
(click to start video clip)