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

2. Agenda Video-Based Eye Tracking Basic Terminology:
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. Mapping raw eye data / camera image data to predict gaze position
Calibration
Mapping raw eye data / camera image data to predict gaze position
-calibration samples from raw camera image space with pupil position “D” are overlaid on top of a view of what the subject sees
-target location gives an idea of where in the raw camera space the subject should be looking
-calibration targets as they are acquired give insight into adequacy of the sampled positions and progress of the calibration

5. Good Calibration Poor 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. Checking accuracy level of the calibration
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, ° 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= Hz
1.8 ms delay (SD= Hz
No missing data after blinks

12. EyeLink Desktop Mount

13. EyeLink 1000 Remote Mode

14. EyeLink 1000 Remote Mode Accurate: No Head Stabilization required:
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 Setup Tower 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 Setup Desktop 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. Search Limits: when to use and how to enable
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. Adjusting Search Limits
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 model fitting:
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. Focusing the Eye Camera
Participant Setup
Focusing the Eye Camera
Focusing Arm Focused Not Focused

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

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

34. Participant Setup
Binocular vs. Monocular Mount

35. Subjects wearing glasses
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 Setup EyeLink 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 Setup EyeLink 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 Setup EyeLink Remote
Target is too close to the eye vertically Target has a large angle

40. Participant Setup EyeLink 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 Setup EyeLink 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 Setup EyeLink 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. Good Calibration Poor 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. Checking gaze accuracy of the calibration
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) What’s recorded?
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
(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
ESACC L …
SSACC L
ESACC L
(Please read Chapter 4 of EyeLink 1000 User Manual)

51. EyeLink Recording Data
Fixations
SFIX: eye, start time
EFIX: eye, start time, end time, duration, average x/y, pupil size, and additionally, resolution.
SFIX L
EFIX L
...
SFIX L
EFIX L
(Please read Chapter 4 of EyeLink 1000 User Manual)

52. EyeLink Data Viewer

53. EyeLink Data Viewer Excellent Data Visualization
Spatial Overlay, Temporal Graph, and Playback Views
Flexible Event Filtering
Fixations, Saccades, Blinks, Interest Areas, etc.
Reaction Time Definition, Interest Period Definitions
Detailed Output Reports
Fixation, Saccade, Interest Area, Trial, Message, or Sample Reports
Full Experiment Integration by Messages
Images, Interest Areas, and Trial Condition Variables

54. EyeLink Data Viewer
Generates detailed Fixation, Saccade, Interest Area and Trial reports

55. EyeLink Support Documents
EyeLink 1000 User Manual
EyeLink 1000 Installation Guide
SR Research Experiment Builder
Windows Programmers Guide
EyeLink Data Viewer
Contact Information
Phone: /
Web:

56. EyeLink Support