Eye Movement and Glance Tracking - TUM€¦ · Eye Movement and Glance Tracking Valentin Shopov...

Chair for Computer Aided Medical Procedures & Augmented Reality | campar.in.tum.de

4 May 2007

Department of Informatics | Technische Universität München

FachgebietAugmented Reality

Eye Movement and Glance Tracking

Valentin [email protected]

CAMP-AR | Department of Informatics | Technische Universität München | 4 May 2007 2

Chair for Computer Aided Medical Procedures & Augmented Reality | campar.in.tum.de FachgebietAugmented Reality

Overview

IntroductionEye movementsEye movements - indicator for mental activityEye trackingVideo-based tracking

head-mounted systemsenvironmentally fixed systems

Pupillometry



Overview



Pupillometry



Motivation

Can we measure usability?

Can we measure distraction?Information Overload (IO)Change Blindness (CB)Perceptual Tunneling (PT)Cognitive Capture (CC)



Introduction

visionhighly complex processlarge amount of information

human visual systemeyesoptic nervesbrain



The Human Eye

similar mechanismfound in cameras

anatomy of the human eye



Visual Fields

3 visual fieldsfoveal: < 2 °parafoveal: < 10 °peripheral: 10 - 30 °

the three visual fields



Overview



Pupillometry



Types of Eye Movement

eye movements

voluntaryunvoluntary

• saccades• smooth pursuit• vergence

fixationalmovements

gaze shiftingmovements

gaze stabilizingmovements

• drifts• microsaccades• microtremor

• vestibo-ocularreflex (VOR)

• optokinetic reflex



Saccades vs. Smooth Pursuit

primary purpose of saccadeslocating new points of interestonly for steady objects

primary purpose of smoothpursuit

following moving objects

videos by Micromedical Technologies Inc.



Saccades and Fixation

fixationperiod between two consecutive saccadestypical duration: 200 - 600 ms

visual perception in humansonly during a fixationno perception during saccades

fixation fixation fixation…saccade saccade



Saccades

quick, simultanious movements of both eyes in the samedirectionballistic

cannot be suppressed once initiatedcommon values

duration: 10 - 80 msamplitude: 2 - 50 °angular velocity: ~ 1000 °/s



Saccades, Fixations and Reading

study of speed reading made by Humanistlaboratoriet, Lund University



Overview



Pupillometry



Eye Movement and Mental Activity

relationship firstdemonstratedby Yarbus (1967)



Impact of Mental Workload on Visual Activity

… when workload increased

median fixation time increase

median amplitude of saccade decrease

saccades per time unit decrease



Characteristics of Glance Behaviour

amount of glancesreduced amount of glances may be an indicator for cognitivecapture (CC)

percentage of non task relevant glancesavailable after classification of the glances

maximum glance durationaccumulated glance durationmedian glance duration

during a seconadary task



Overview



Pupillometry



Methods for Eye Movement Measurement

subjective measurement

contact-based measurement

video-based measurement



Subjective Approach

very simple techniquebased on

direct observation orsubject‘s description of whathe‘s seeing (experiments withafterimages)

Staring at the light bulb for 30 s will cause an afterimage of a glowing light bulb!



Contact-based Approach

search coilinduced electric currentdue to eye movementin a magnetic field

electrooculographymeasurement of the potential differencebetween corneaand retina



Overview



Pupillometry



Video-based Eye Tracking

eye tracking system

off-line unitrecording unit

raw data

processing unit

processed data analyzed data



Video-based Eye Tracking

Requirementsrobusteasy to calibratehigh sample ratescomfortable for userslittle influence on glance behaviour



Video-based Eye Tracking Standards

StandardsCCIR Standard (Europe):

625 lines50 frames/s → 25 images/s

NTSC Standard (USA, Japan):525 lines60 frames/s → 30 images/s



Types of Eye Tracking Systems

head-mounted systems+ precise- intrusive (may alter normal glance behaviour)

environmentally fixed systems+ non-intrusive (do not affect normal glance behaviour)- less accurate



Head-mounted Systems

illumination with infrared (IR) lighteye serves asretroreflector



Eye Tracking Techniques

bright pupil

on-axis IR light source

+ detailed iris pigmentationinformation

+ applicable in variouslighting conditions

- not suitable for outdoortracking ← interference

dark pupil

off-axis IR light source

less precise alignmentrequiredno interference even forlarge eye movementsreduced quality of image



Overview



Pupillometry



Eye Tracking with Artificial Neural Networks

Inputretinal image

Outputgaussian distributionof the x and y coordinatesof the gaze vector

3 layer networkstandard backpropagationalgorithm



Eye Tracking with Active Appearance Models

image interpretationusing statistical models



Overview



Pupillometry



Pupil Size

1.5 mm ← 5 mm → 8 mmbright light standard dim light

factors that cause change in pupil size

brightness

drugsalcohol illness

emotionslikes/dislikes

physicalactivity

mental workload

age



Basic Principles of Pupillometry

observation I:Brightness has the biggest influence on pupil size.

observation II:Every change in pupil size occurs independently

from other changes. (linear combination of changes)

observation III:Pupil size increases proportionally to the difficulty level

of the task to be solved.



Experimental Results

pupil size in different driving situations

picture taken from R

ößger



Eye Tracking and Time-critical Tasks

evaluation of pilots

driving



Other Application Areas

car design

marketing research



Conclusion

Can we measure usability?

Can we measure distraction?Information Overload (IO)Change Blindness (CB)Perceptual Tunneling (PT)Cognitive Capture (CC)

Yes!

Yes!



Thank you for your attention!

Eye Movement and Glance Tracking - TUM€¦ · Eye Movement and Glance Tracking Valentin Shopov...

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