EyeLink 1000/2k and EyeLink Remote Introduction and Training

1. EyeLink 1000/2k andEyeLink Remote Introduction and Training SR Research Ltd. Toronto - Ottawa, Canada

2. Agenda • Video-Based Eye Tracking • pupil image • corneal reflection • Basic Terminology: • calibration and validation • spatial and temporal resolution • accuracy • The EyeLink CL Platform • overview • camera mount types • EyeLink Remote mode • EyeLink Components • Practical Issues • the Set Options screen • camera setup and recording

3. Video-Based Eye Tracking • infrared light and camera • -minimal interference with the visual stimulus • high-speed video image analysis • -dark pupil based • -corneal reflection based • -determine pupil and CR centers • calibration yields predictive model • -sample the camera image while subject fixates • different known locations • -induce a predictive model • validation evaluates model

4. Calibration Mapping raw eye data / camera image data to predict gaze position

5. Calibration Calibration Grid gives idea of quality of the underlying predictive model Good Calibration Poor Calibration

6. Video-Based Eye Tracking • Validation • -evaluate predictive model test-retest accuracy • -subject re-fixates known locations • -difference between the predicted gaze position and • validation sample is ‘accuracy’ • -summarizes calibration adequacy • -reveals spatial positions fit least accurately as error • in degrees of visual angle

7. Validation Checking accuracy level of the calibration

8. Some Basic Terms • Accuracy • -test-retest discrepancy • -measure of absolute spatial location • -will be best with dominant eye • Spatial Resolution • -smallest measureable movement • -measure of relative spatial location • -worsens with faster sampling rate and • obstacles such as glasses • Temporal Resolution • -how many images processed per second (Hz) • -also referred to as ‘samples’ per second

9. More Basic Terms • Eye Event Resolution • -smallest psychological event that is spatially • measurable with the system • Blink Recovery Time • -recover of gaze position after missing data • Head Movement Compensation • -tolerable level of head movements

10. EyeLink 1000 Family • Focal Imaging Technology (FIT) • point, focus and track camera • real-time Host computer for data collection • Display computer for stimulus delivery • One Camera, Many Mounts… • -Desktop, Tower, Primate, Arm Mount • -Long Range variants for MEG/MRI • … and Multiple Modes of Operation • -High Precision Monocular/Binocular • -Remote Mode with Head Free to Move • Unified Software • Host Eye Tracker Application • Application Programming Interface

11. EyeLink 1000 High Precision • Accurate: • Drift free, 0.25 - 0.5° typical • approx 2 cm lateral head movement compensation • Highest Spatial Resolution available, Low Noise: • 0.01° RMS in pupil-CR 1000 Hz tracking mode • 0.02° RMS in pupil-CR 2000 Hz tracking mode • glasses increase error by about 0.01° • Fastest Sampling Rate Available: • 2000 / 1000 / 500 / 250 Hz recording • Eye Event Resolution: • 0.05° microsaccades • Real-Time streaming data via Ethernet or analog: • 1.4 ms delay (SD=0.4 ms) @ 2000 Hz • 1.8 ms delay (SD=0.8 ms) @ 1000 Hz • No missing data after blinks

12. EyeLink Desktop Mount

13. EyeLink 1000 Remote Mode

14. EyeLink 1000 Remote Mode • Accurate: • 0.25°-0.5° average accuracy • No Head Stabilization required: • 22 x 18 x 20 cm (horizontal x vertical x depth) allowable head movement at a 60 cm camera distance • Spatial Resolution: • 0.1° RMS error • Fastest Sampling Rate of any Remote System: • 500 Hz monocular eye tracking • No missing data around blinks • Real-time: • Access eye position data with 3.0 ms delay (SD=1.11 ms)

15. EyeLink System Components

16. The Display PC • Performs full experiment control • - integrates calibration and data collection into one step • - sets any tracker preference • sends commands to control tracker • Allows focus on stimulus presentation and data processing • ordinary experiment delivery with calls to the underlying • EyeLink libraries to interface with the eye tracker • Time stamps experiment events with messages • near Real-time access to eye sample and eye event data • structures for gaze contingent paradigms

17. Display PC API • Compatible with many stimulus delivery methods: • Experiment Generator Packages: • -Experiment Builder • -E-Prime • -Presentation • -Psychtoolbox (MATLAB) • Programming Languages: • -C / C++ • -Python • -Delphi • -any Windows COM language • Multiple Operating Systems: • MacOS X • Windows • Linux

18. The Host PC • Host PC Application controls the eye tracker • Performs image analysis • Performs data recording • Performs eye event parsing • Configures preferences • Provides real-time feedback • Gaze view: Gaze cursor on background image • Plot view: Eye traces over time

19. Recording Gaze View

20. Recording Plot View

21. The Host PC Application Set Options Screen

22. The Host PC Application Set Options Screen

23. Participant Setup Camera Setup Screen

24. Participant SetupTower Mount • set the height of the chair, chinrest and Tower Mount so your subject is comfortably seated and looking at the top of the display • -never adjust the Tower Mount with subject’s head in place • set the eye-selection knob to track the dominant eye • adjust the mirror angle to get a good view of the eye, or to avoid glasses reflections; adjusting chin position may help too • click pupil in the global view to autothreshold (Host Display PC) • focus the camera - minimize size of yellow CR circle • autothreshold and if necessary, adjust pupil and CR thresholds • -if cautious or troubleshooting, check the setup by asking the subject to look at four corners while monitoring threshold quality at all positions • calibration, validation and recording

25. Participant SetupDesktop Mount • set the height of the chair and chinrest so your subject is comfortably seated and looking at the top of the display • center the Desktop Mount at the bottom of the display as high in the field of view as possible without occluding the display • - ensure you have the correct lens and camera angle for the type of tracking you wish to perform (monocular, binocular or remote) • adjust camera angle and position to get a good view of the eye(s) • click pupil in the global view to autothreshold (Host or Display PC) • focus the camera - minimize size of yellow CR circle • autothreshold and if necessary, adjust pupil and CR thresholds • -if cautious or troubleshooting, check the setup by asking the subject to look at four corners • -if the CR is smeared move the Desktop Mount toward the problematic corner until CR is tracked • calibration, validation and recording

26. Participant Setup Optimal Eye Position • adjust the height of the chair so that the subject is comfortable and has line of sight to upper part of the monitor • the forehead rest should be just above the eye brow. The figures on the right shows that the subject is seated too high (top-right) or too low (bottom-right).

27. Participant Setup Search Limits: when to use and how to enable • Search Limits (red box) can be used to reduce the area of the image that is searched to find the eye • normally Search Limits is not needed, however with some participants glasses it can be used to exclude regions of the camera image that may otherwise be detected as a pupil or CR

28. Participant Setup Adjusting Search Limits • Press “Use Search Limits” to toggle on /off search limits. • Use ALT and cursor keys to adjust the shape of the search limits. • Use SHIFT and cursor keys to adjust the position of the search limits.

29. Participant Setup Centroid Vs. Ellipse Pupil Tracking Modes • Centroid model fitting: • - tracks centre of a circle fit to thresholded pupil • advantages: • highly stable • has very low noise • - disadvantage: position drift if pupil is occluded (i.e., by eyelids) • Ellipse model fitting: • - tracks centre of an ellipse fit to the thresholded pupil • -advantages: • - decreased drift • - overcomes pupil occlusion • -disadvantage: higher noise level

30. Participant Setup Focusing the Eye Camera Focusing Arm Focused Not Focused

31. Participant Setup Setting Pupil Threshold Figure 1 The pupil threshold can be adjusted automatically, through the Auto-threshold command, or manually, through the up/down arrow. A threshold too low will result in shadows (Figure 1), while a threshold too high will result in a noisy signal (Figure 2). Figure 2

32. Participant Setup Symptoms of Poor Pupil Threshold Pupil clipped and lost Good Corner Shadow captures pupil

33. Participant Setup Setting Corneal Reflection (CR) Good Corneal Reflection Poor Corneal Reflection

34. Participant Setup Binocular vs. Monocular Mount

35. Participant Setup Participant Setup Subjects wearing glasses Binocular Setup Good mirror angle Poor mirror angle

36. Status Panel Monitor the status of camera image of the tracked eye throughout setup, calibration, validation and recording phases. Pupil OK (green): Pupil present and can be tracked at selected sample rate SIZE (yellow): Occurs when the pupil size is larger than the maximum allowed pupil size MISSING (red): Pupil not present Corneal (only operational in Pupil-CR mode) OK (green): Corneal reflection is present and can be tracked MISSING (red): Corneal reflection is not present

37. Participant SetupEyeLink Remote • set the height of the chair so your subject is comfortably seated • center the Desktop Mount at the bottom of the display as high in the field of view as possible without occluding the display • place the target on the subject’s forehead • adjust camera angle and position to get a good view of the eye and sticker; capture as wide a range of subject movement as possible • click pupil in the global view to autothreshold (Host Display PC) • focus the camera - minimize size of yellow CR circle • adjust thresholding bias for pupil and CR • -if cautious or troubleshooting, check the setup by asking the subject to look at four corners • -if the CR is smeared move the Desktop Mount toward the problematic corner until CR is tracked • calibration, validation and recording

38. Participant SetupEyeLink Remote • place target sticker on the subject’s forehead • the eye and the sticker stay within the camera image when the subject’s head moves • an ideal target-camera distance should be about 550 mm to 600 mm for calibration • for highest accuracy use a 13 pt calibration

39. Participant SetupEyeLink Remote Target is too close to the eye vertically Target has a large angle

40. Participant SetupEyeLink Remote Pupil threshold bias adjusted by UP or DOWN cursor keys (1.08 typical) CR threshold bias adjusted by – or + keys (1.00 typical) .

41. Participant SetupEyeLink Remote • Monitor the thumbnail camera images at the lower left corner of the tracker screen • The two dots in the middle panel reflect the target and eye position in the global camera image • For reliable tracking, both dots should stay within the red box.

42. Participant SetupEyeLink Remote Pupil OK: Pupil present and can be tracked at selected sample rate SIZE: Occurs when the pupil size is larger than the maximum allowed pupil size or smaller than the required size (e.g., too bright or small pupil) MISSING: Pupil not present Status Panel Corneal OK: Corneal reflection is present and can be tracked MISSING: Corneal reflection is not present Target OK: Target is present and can be tracked MISSING:Target is not present. NEAR EYE: Target is placed too close to the eye on the vertical dimension. ANGLE: Target has too large an angle to be recognized properly.

43. Calibration

44. Calibration Always checks for the calibration grid at the end of calibration. Good Calibration Poor Calibration

45. Calibration Improving calibration accuracy: • check pupil and CR as the subject looks at all four corners of the display – they should always be visible, well- thresholded and tracked • encourage the subject to sit still – no head turning! • use backspace (to redo a target) and manual accept mode (spacebar twice) to only sample the eye position when the subject is stably fixating the calibration target • match the background color of the screen during calibration/validation to your test displays; -changes in pupil size caused by large brightness differences will reduce recording accuracy

46. Validation Checking gaze accuracy of the calibration

47. Validation • Validation Results: • GOOD (green background): Errors are acceptable. • FAIR (grey background): Errors are moderate, calibration • should be improved. • POOR: (red background): Errors are too high for useful • eye tracking. • In general, ensure that the average gaze error is within 0.5 and maximum error within 1.0

48. EyeLink Data • EDF File (binary File) • Use EDF2ASC converter to get ASC files • Use EyeLink Data Viewer for direct analysis • What’s recorded? • Samples • Events • Saccades • Fixations • Blinks • Messages • Buttons • (Please read Chapter 4 of EyeLink 1000 User Manual)

49. EyeLink Recording Data • Samples • System time, x, y and pupil size • With optional velocity, resolution, and CR status • 6079861 503.7 680.3 972.0 ..... • 6079862 503.7 680.1 972.0 ..... • 6079863 503.8 680.1 972.0 ..... • 6079864 503.8 680.2 972.0 ..... • 6079865 503.9 680.2 971.0 ..... • 6079866 503.7 680.1 971.0 ..... • 6079867 503.7 680.1 971.0 ..... • 6079868 503.6 680.0 970.0 ..... • 6079869 503.6 680.1 970.0 ..... • 6079870 503.7 680.2 970.0 ..... • (Please read Chapter 4 of EyeLink 1000 User Manual)

50. EyeLink Recording Data • Saccades • SSACC: eye, start time • ESACC: eye, start time, end time, duration, start x/y, end x/y, amplitude, peak velocity. • SSACC L 6079955 • ESACC L 6079955 6079962 8 507.5 682.5 511.9 682.0 0.20 38 • … • SSACC L 6080723 • ESACC L 6080723 6080763 41 513.8 679.7 633.5 550.5 7.94 285 • (Please read Chapter 4 of EyeLink 1000 User Manual)