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Survey of Eye Tracking Techniques

PSYC 736 – Spring 2006. Survey of Eye Tracking Techniques. 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.

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Survey of Eye Tracking Techniques

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  1. PSYC 736 – Spring 2006 Survey of Eye Tracking Techniques 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

  5. 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. 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.

  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. 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 Electrooculogram (EOG)

  10. -based on current flow through induction loop -good temporal resolution (pulsed; 1000 Hz) -supreme spatial resolution (< 10 arcsec) -uncomfortable -easily accommodates animal research Scleral Search Coil

  11. -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 Scleral Mirror(Yarbus, 1967)

  12. -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 Limbus Tracker

  13. -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) Corneal Reflection Technique(s) Dark Pupil

  14. - 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) ASL Model 501(USD Vision Lab)

  15. Corneal Reflections/Calibration

  16. 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)

  17. USDInstrumented Research Vehicle

  18. ASL ETS-PCDriver 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

  22. Corneal Reflections/Calibration

  23. Some ExamplesofDriver Eye Movement Records

  24. SD HWY 50 West

  25. Main Street - Vermillion

  26. Cherry StreetSlow Moving Vehicle

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

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

  29. -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 Dual Purkinje Eye Tracker Courtesy of Jochen Triesch, UCSD

  30. 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

  31. Older Driver Performance MetricsInternet-in-the-Car (Driver Distraction) video clip next screen

  32. Older Driver Performance MetricsInternet-in-the-Car (Driver Distraction) (click to start video clip)

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