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How eyetrackerswork


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  • 1. Association for Business Communication 78th Annual International Convention New Orleans, 2013 Tharon Howard, Clemson University UsabilityTesting Facility Director
  • 2. Part One: An Introduction to Eye Tracking Foundational Concepts and Two Approaches to Website Navigation (Tharon) Part Two: Webby Awards and an Eye Tracking Study (Heather) Part Three: Limitations and Strengths of Eye Tracking (Brian)
  • 3. Fovea Saccades Fixations Parafovea How FovealVisionWorks
  • 4. Example of FovealVision Source:
  • 5. FovealVision Instead of: Credit: Dan Liddle, Clemson UTF
  • 6. FovealVision We can only see: Credit: Dan Liddle, Clemson UTF
  • 7. FovealVision We can only see: Credit: Dan Liddle, Clemson UTF
  • 8. FovealVision We can only see: Credit: Dan Liddle, Clemson UTF
  • 9. FovealVision We can only see: Credit: Dan Liddle, Clemson UTF
  • 10. Saccades and Fixations Can be as short as 20 milliseconds or as long as 200 milliseconds The fastest movement produced by the human body Substantial image blur during a saccade due to this speed fixation fixation saccade Fixation: Eye-movement pauses to acquire Content Saccades: The period of eye-movement from one fixation to the next
  • 11. AlfredYarbus –TheVisitor (1967) Saccades are not arbitrary; they’re influenced by parafovea vision Users’ tasks and goals play a significant role in the gaze plot
  • 12. “Depth of Processing” Gaze Plot
  • 13. • “Mechanical” or Search Coil • “Glint” or Dual Purkinje • Limbus or PupilTracking • Dual-PointVideo Popular EyeTracking Technologies to Consider
  • 14. Search Coil & Magnetic Field or “Mechanical” Uses contact lenses with search coils and a magnetic field Usually combined with reflected light Extremely accurate Very costly Uncomfortable & not portable Source:
  • 15. Dual Purkinje Image or “glint” Uses infrared light to create reflections from different parts of eye Video tracks 2 reflections and software calculates angles Good accuracy Comfortable for users Allows more head movement Still costly Source: Source: Sanson+mirror+images
  • 16. Limbus or PupilTracking or “Single-PointVideo-Based” Image processing of video is used to locate pupil and calculate POG A Starburst algorithm projects rays from an initial starting point detecting pixels with high image gradients Source: Howard & Sulak Example of rays projected from initial point Source: Ryan, Duchowski, & Burchfield
  • 17. “Dual-PointVideo-Based” Image processing tracks pupil and corneal reflection of IR light is also tracked Less expensive Comfortable Head movement is limited Only accurate to 1-2 degrees (1o is about 0.5” at 27” distance) Example of rays projected from initial point Source: Ryan, Duchowski, & Burchfield Source: Howard & Sulak
  • 18. Some OtherTerms to Know Accuracy—Measured in degrees and typically ranges from 0.5 to 2 degrees. Keep in mind that 1o is about half an inch of resolution at the normal 27” viewing distance for computer monitors. Precision—Smallest change in eye position that can be measured. Usually this is also measured in fractions of degrees. Sampling Rate—Measured in Hertz, this factor is important because eye movements are the fastest humans can produce. Over 1000 Hz is needed to capture many eye movements, but most systems typically run at 50 to 60 Hz.
  • 19. The “F Pattern” and Golden Triangle Source: tracking-google-through-the-years/ Source: “Eyetracking visualizations show that users often read Web pages in an F-shaped pattern: two horizontal stripes followed by a vertical stripe.” Jakob Nielsen “We recorded how 232 users looked at thousands of Web pages.We found that users' main reading behavior was fairly consistent across many different sites and tasks.” Found consistent pattern from 2005 - 2011
  • 20. Rosenblatt and Web Page Genres Efferent(to carry away) Aesthetic (emotional pleasure) “In readings that fall somewhere in the efferent half of the continuum, the reader selects out predominantly more public or cognitive elements than private.The aesthetic stance, in contrast, accords selective attention to predominantly more of the penumbra of private feelings, attitudes, sensations, and ideas than to the public aspects.” Louise Rosenblatt Source: “TheTransactionalTheory:Against Dualisms.” College English,Vol. 55, No. 4. (Apr., 1993), p. 383.
  • 21. Rosenblatt and Gaze Plots Efferent(to carry away) Aesthetic (emotional pleasure) Do the GoldenTriangle and F-Pattern obtain for “aesthetic” sites as well as for “efferent” sites?
  • 22. Tharon Howard, Clemson UsabilityTesting Facility Director Part One
  • 23. Brian Gaines, Graduate Research Assistant, Clemson University
  • 24. EyeTrackers can be expensive.This usedTobii T120 system is $27,500. (Image courtesy of eBay, inc.) SensoMotoric Instruments (SMI) Eye Tracking Glasses 2.0 are priced on a case by case basis.This could potentially be quite costly. (Image courtesy of SensoMotoric Instruments, GmbH) Price
  • 25. Lab costs, as well as the costs for participants can be costly. For example, Eye Tracking, Inc. charges between $5,000-$250,000 per study.These costs are determined by the type of study, length of study, number of participants, etc. Price
  • 26. The Grinbath Eye Guide is roughly $2,495, with discounts applied to multiple unit purchases. (Image courtesy of Grinbath, LLC) Affordable options are available.
  • 27. Eye Tribe’s USB 3.0 Hardware is only $99, but comes with a Software Development Kit (SDK), which means code must be written in order for this device to be used. While the base price is attractive, the time and cost of hiring a software engineer is something to consider. But, how affordable is affordable?
  • 28. Equipment Sensitivity Because of the sensitivity of the equipment, the participants were uncomfortable. (Image Courtesy of Brian Gaines)
  • 29. Equipment Sensitivity Calibrating the eye tracker is in itself an art and a science. (Image courtesy of Tharon W. Howard, Ph.D.)
  • 30. Equipment Sensitivity
  • 31. Differences in Participants
  • 32. Retrospective think aloud is a technique used in usability, and eye tracking in particular, to gather qualitative information on the user intents and reasoning during a test. It's a form of think aloud protocol performed after the user testing session activities, instead of during them. Fairly often the retrospective protocol is stimulated by using a visual reminder such as a video replay. (Guan, Lee, Cuddihy, and Ramey, 2006) Stimulated RetrospectiveThink Aloud
  • 33. More than 80% of subjects’ verbalizations of what they were attending to corresponded with the eye movement data. We reject the notion of subjects’ fabrication since only less than 3% of their verbalization failed to match up with objects identified by their eye movement. (Guan, Lee, Cuddihy, and Ramey, 2006) Stimulated RetrospectiveThink Aloud
  • 34. Immediately following the eye tracking session, the data is available. Instantaneous Results
  • 35. Instantaneous Results
  • 36. Cons • Certain eye tracking technologies are expensive • Lab/participants costs • Equipment sensitivity • Accommodating for differences in participants Pros • As technology advances, prices will drop • Stimulated Retrospective Think Aloud is a valid data collection method • Results are intantaneous Conclusions