Survey of Eye Tracking Techniques

Observable(Quantifiable)

Eye MovementsCovert

Information Processing

PSYC 736 – Spring 2006

Introduction

Acuity as a function of retinal location

Visual acuity drops off rapidly from the fovea to the visual periphery as shown in thisfigure.

The best visual acuity is found in a parafoveal area of 1-4 degrees from the fovea. (adapted from Schmidt and Connolly, 1966)

Photographic Simulation ofVariable Retinal Spatial Resolution

Courtesy of Stuart Anstis

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 ballThe 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. Abscissas-duration 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)

Dark Pupil

Bright Pupil(Coaxial IR Illumination)

-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

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 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)

USDInstrumented

Research Vehicle

ASL ETS-PCDriver 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 Examplesof

Driver Eye Movement Records

SD HWY 50 West

Main Street - Vermillion

Cherry StreetSlow Moving Vehicle

Saccade Detection Latency ComparisonASL 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)

Schieber, et al., 1997

Accuracy MapSubjective Estimation of In-Vehicle Gaze Position

(Camera position: 65-deg from L.O.S)

Older Driver Performance MetricsInternet-in-the-Car (Driver Distraction)

video clip next screen

Older Driver Performance MetricsInternet-in-the-Car (Driver Distraction)

(click to start video clip)