Development of an Eye TrackerDevelopment of an Eye Tracker

By Jason Kajon BarrettBy Jason Kajon Barrett

of the Center for Imaging Scienceof the Center for Imaging Science

at the Rochester Institute of at the Rochester Institute of TechnologyTechnology

Advisor: Jeff PelzAdvisor: Jeff Pelz

What is an Eye Tracker?What is an Eye Tracker? A device used to detect eye motion.A device used to detect eye motion.

What are they for ?What are they for ?

• Access for the physically handicapped, Access for the physically handicapped,

• target variable resolution,target variable resolution,

• realistic virtual reality environments,realistic virtual reality environments,

• and increased bandwidth of human-computer and increased bandwidth of human-computer interaction. Shannon’s Rule: C = BW log interaction. Shannon’s Rule: C = BW log22(1 + S/N)(1 + S/N)

Types of TrackersTypes of Trackers: :

• mechanical- corneal covermechanical- corneal cover

• magnetic- eyeball polaritymagnetic- eyeball polarity

• electric- EMG & EOGelectric- EMG & EOG

• optical- IR illuminationoptical- IR illumination

What is the Research Design?What is the Research Design?

A device using four IR photodetectors and a A device using four IR photodetectors and a microcontroller to detect the onset of rapid eye microcontroller to detect the onset of rapid eye motion. A PicBasic program to run this device.motion. A PicBasic program to run this device.

Why a microcontroller ?Why a microcontroller ?

• Simple data manipulation, Simple data manipulation,

• lookup table,lookup table,

• single upgradable chip,single upgradable chip,

• cost for device,cost for device,

• and ease burden on CPU.and ease burden on CPU.

Targets for the ResearchTargets for the Research

• 500 Hz Sampling Rate500 Hz Sampling Rate

• < $300 Project Expense< $300 Project Expense

• < 4 Degrees Accuracy< 4 Degrees Accuracy

Budget: ( Digi-Key, 1997 )

One Microchip 20 MHz microcontroller w/ 8 bit A/D ConverterPIC16C74A/JW-ND @ 18.77 each

$18.77One Microchip PIC16C7X Family Data Book

92678-ND @ $6.95 each $6.95

One CTS 20 MHz Microprocessor CrystalCTX062-N2 @ $1.74 each $1.74

One Power-One +5V Power SupplyPW9906-ND @ $109.72 each

$109.72One Burr-Brown CMOS 8 bit Buffered Digital-to-Analog Converter

DAC7528P-ND @ $6.30 $6.30

One Linear Technology Precision Voltage ComparatorLT1013ACN8-ND @ $7.13

$7.13One Burr-Brown Differential Precision Gain Amplifier

1NA105KU-ND @ $5.24 $5.24

8 – ¾” Rectangular / Multiturn ( 15 )Cermet/Industrial/Sealed Potentiometers3009P-103-ND @ $2.16 each

$17.2816 QT Optoelectronics Semiconductor Infrared Emitters

( IRED LED’s ) 1N6266QT-ND @ $4.15 each$66.40

16 QT Optoelectronics Semiconductor Infrared Photo DetectorsBPW38QT-ND @ $2.73 each

+ $43.68

Total $283.21

Initial BudgetInitial Budget• Microcontroller and instructionsMicrocontroller and instructions $ 25$ 25

• CrystalCrystal $ 2$ 2

• Power SupplyPower Supply $110$110

• ComparatorComparator $ 7$ 7

• Diff. OP-AMPDiff. OP-AMP $ 5$ 5

• PotentiometersPotentiometers $ 20$ 20

• IR EmittersIR Emitters $ 67$ 67

• IR Detectors IR Detectors $ 45$ 45

• TotalTotal $281$281

Targets for the ResearchTargets for the Research

• 500 Hz Sampling Rate500 Hz Sampling Rate

• < $300 Project Expense< $300 Project Expense

• < 4 Degrees Accuracy< 4 Degrees Accuracy

Why 500 Hz ?Why 500 Hz ?• SaccadesSaccades- rapid eye movements rapid eye movements

• last 30 - 120 ms, last 30 - 120 ms,

• cannot be within 100 ms of eachothercannot be within 100 ms of eachother

• videovideo eye tracking unit at 60 Hz eye tracking unit at 60 Hz (i.e. 17 ms, half a short saccade.) (i.e. 17 ms, half a short saccade.)

For a 20 MHz PIC16C74A/JW-ND processor

Sampling RateSampling Rate

• 200 200 sec / instructionsec / instruction

• 200 instructions200 instructions

• 40 40 sec for samplesec for sample

• 50 kHz50 kHz sample rate sample rate

For a 10 MHz PIC16C84 processor

Sampling RateSampling Rate

• 20 20 sec / instructionsec / instruction

• 100 instructions100 instructions

• 2 msec for sample2 msec for sample

• 500 Hz500 Hz sample rate sample rate

Targets for the ResearchTargets for the Research

• 500 Hz Sampling Rate500 Hz Sampling Rate

• < $300 Project Expense< $300 Project Expense

• < 4 Degrees Accuracy< 4 Degrees Accuracy

The The foveafovea covers approximately a 1 covers approximately a 100 Field of View. Video eye trackers can Field of View. Video eye trackers can come to within 1/2 come to within 1/2 0 0 for field of view. for field of view. The main consideration is speed.The main consideration is speed.

Why 4 Degrees?Why 4 Degrees?

To get within 4 Degrees:To get within 4 Degrees:

• individualindividual calibration calibration will be necessary will be necessary

• extensive extensive lookup tablelookup table creation creation

• consecutiveconsecutive ON/OFF ON/OFF state comparison state comparison ( provided for by software )( provided for by software )

Sample Calibration TargetSample Calibration Target

(with Nine Targets)(with Nine Targets)

Sample Calibration TargetSample Calibration Target

(with Seventeen Targets)(with Seventeen Targets)

The Proposed DesignThe Proposed Design

• ASL Model 210 Eye ASL Model 210 Eye Movement MonitorMovement Monitor

• made from scratchmade from scratch

• single eye single eye measurementmeasurement

• fit within HMDfit within HMD

HorizontalHorizontal++__

VerticalVertical | ? || ? |

ASL model 210 eye movement monitorASL model 210 eye movement monitor

Horizontal MeasurementHorizontal Measurement

++__

•Negative measurement = leftNegative measurement = left

•Positive measurement = rightPositive measurement = right

Detector Positions as the Detector Positions as the Viewer Shifts Their Viewer Shifts Their

Horizontal GazeHorizontal Gaze

RightRight CenterCenter LeftLeft

Vertical MeasurementVertical Measurement

| ? || ? |

•High measurement = upHigh measurement = up

•Low measurement = downLow measurement = down

Detector Positions as the Detector Positions as the Viewer Shifts Their Viewer Shifts Their

Vertical GazeVertical Gaze

UpUp CenterCenter DownDown

ASL video eye trackerASL video eye tracker

Long-term Goals of the Research

•Use in future projects involving Use in future projects involving eye eye contingent updatingcontingent updating and the study of and the study of perceptionperception..

• Measurement of Measurement of saccadicsaccadic eye eye movements.movements.

ConclusionsConclusions

The eye tracker proposed is possible The eye tracker proposed is possible for the proposed for the proposed expenseexpense as there is as there is an adequate sacrifice for an adequate sacrifice for accuracyaccuracy of of eye position to increase the eye position to increase the speedspeed..

The resultant code written in The resultant code written in PicBasic will satisfy the design PicBasic will satisfy the design proposed. proposed.