EyeLink 1000/2k and
EyeLink Remote
Introduction and Training
SR Research Ltd.
Toronto - Ottawa, Canada
Agenda
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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
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
Calibration
Mapping raw eye data / camera image data to predict gaze position
Calibration
Calibration Grid gives idea of quality of the underlying predictive model
Good Calibration
Poor Calibration
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
Validation
Checking accuracy level of the calibration
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
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
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
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
EyeLink Desktop Mount
EyeLink 1000 Remote Mode
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)
EyeLink System Components
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
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
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
Recording
Gaze View
Recording
Plot View
The Host PC Application
Set Options Screen
The Host PC Application
Set Options Screen
Participant Setup
Camera Setup Screen
Participant Setup
Tower Mount
1) 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
2) set the eye-selection knob to track the dominant eye
3) adjust the mirror angle to get a good view of the eye, or to avoid
glasses reflections; adjusting chin position may help too
4) click pupil in the global view to autothreshold (Host Display PC)
5) focus the camera - minimize size of yellow CR circle
6) 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
7) calibration, validation and recording
Participant Setup
Desktop Mount
1) set the height of the chair and chinrest so your subject is comfortably
seated and looking at the top of the display
2) 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)
3) adjust camera angle and position to get a good view of the eye(s)
4) click pupil in the global view to autothreshold (Host or Display PC)
5) focus the camera - minimize size of yellow CR circle
6) 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
7) calibration, validation and recording
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).
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
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.
Participant Setup
Centroid Vs. Ellipse
Pupil Tracking Modes
• Centroid model fitting:
• Ellipse model fitting:
- tracks centre of a circle fit to
thresholded pupil
- advantages:
- highly stable
- has very low noise
- tracks centre of an ellipse fit to the
thresholded pupil
-advantages:
- decreased drift
- overcomes pupil occlusion
- disadvantage: position drift if pupil is -disadvantage: higher noise level
occluded (i.e., by eyelids)
Participant Setup
Focusing the Eye Camera
Focusing Arm
Focused
Not Focused
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
Participant Setup
Symptoms of Poor Pupil Threshold
Pupil clipped and lost
Good
Corner Shadow captures pupil
Participant Setup
Setting Corneal Reflection (CR)
Good Corneal Reflection
Poor Corneal Reflection
Participant Setup
Binocular vs. Monocular Mount
Participant
ParticipantSetup
Setup
Subjects wearing glasses
Binocular Setup
Good mirror angle
Poor mirror angle
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
Participant Setup
EyeLink Remote
1) set the height of the chair so your subject is comfortably seated
2) center the Desktop Mount at the bottom of the display as high in
the field of view as possible without occluding the display
3) place the target on the subject’s forehead
4) 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
5) click pupil in the global view to autothreshold (Host Display PC)
6) focus the camera - minimize size of yellow CR circle
7) 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
8) calibration, validation and recording
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
Participant Setup
EyeLink Remote
Target is too close to the eye vertically
Target has a large angle
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) .
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.
Participant Setup
EyeLink Remote
Pupil
OK:
SIZE:
MISSING:
Pupil present and can be tracked at selected sample rate
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)
Pupil not present
Status Panel
Corneal
OK:
MISSING:
Corneal reflection is present and can be tracked
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.
Calibration
Calibration
Always checks for the calibration grid at the end of calibration.
Good Calibration
Poor Calibration
Calibration
Improving calibration accuracy:
• check pupil and CR as the subject looks at all four corners
of the display – they should always be visible, wellthresholded 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
Validation
Checking gaze accuracy of the calibration
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
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)
EyeLink Recording Data
•Samples
• System time, x, y and pupil size
• With optional velocity, resolution, and CR status
6079861
6079862
6079863
6079864
6079865
6079866
6079867
6079868
6079869
6079870
503.7
503.7
503.8
503.8
503.9
503.7
503.7
503.6
503.6
503.7
680.3
680.1
680.1
680.2
680.2
680.1
680.1
680.0
680.1
680.2
972.0
972.0
972.0
972.0
971.0
971.0
971.0
970.0
970.0
970.0
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
(Please read Chapter 4 of EyeLink 1000 User Manual)
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
6079955
6079955 6079962
8 507.5 682.5 511.9 682.0 0.20
38
6080723
6080723 6080763 41 513.8 679.7 633.5 550.5 7.94 285
(Please read Chapter 4 of EyeLink 1000 User Manual)
EyeLink Recording Data
•Fixations
• SFIX: eye, start time
• EFIX: eye, start time, end time, duration, average x/y,
pupil size, and additionally, resolution.
SFIX
EFIX
...
SFIX
EFIX
L 1454748
L 1454748
1454907
160
510.3
4.1
1187
28.45
27.50
L 1454919
L 1454919
1455873
955
514.0
0.3
1361
28.40
27.50
(Please read Chapter 4 of EyeLink 1000 User Manual)
EyeLink Data Viewer
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
EyeLink Data Viewer
Generates detailed Fixation, Saccade, Interest Area and Trial reports
EyeLink Support
• Documents
•EyeLink 1000 User Manual
•EyeLink 1000 Installation Guide
•SR Research Experiment Builder
•Windows Programmers Guide
•EyeLink Data Viewer
• Contact Information
•E-mail: support@sr-research.com
•Phone: 1-613-826-2958/ 1-866-821-0731
•Web: http://www.sr-support.com
EyeLink Support