jochen triesch, uc san diego, triesch 1 eye movements and eye tracking why move the eyes? see the...
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Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 1
Eye Movements and Eye TrackingEye Movements and Eye Tracking
Why move the eyes?• see the same thing better (stabilize image, but not too well!)• see something else (overcome low peripheral resolution)
S. Anstis
• only small part of visual field is sampled at full resolution
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 2
Cortical Magnification in V1Cortical Magnification in V1
Eric Schwartz
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Approximately:
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 3
Types of eye movementsTypes of eye movements
Major Distinctions:• conjugate vs. disjunctive• abrupt vs. slow
Types:• vestibuocular reflex: counteract head rotation• optokinetic reflex: counteract large field retinal motion• smooth pursuit: counteract object motion (<30 deg/s)• saccades: rapidly shift gaze direction (<600 deg/s)• vergence movements: adjust vergence angle• accomodation: adjust focus• microsaccaes: counteract drift during fixation (1-2 Hz, <5’)• microtremor: .5’, 30-100Hz
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 4
SaccadesSaccades
Yarbus (1950s)
• alternations of fixations and saccades, 3 per second
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 5
Yarbus, 1967:• examine the picture at
will• estimate the economic
level of the people• estimate the people’s
ages• guess what the people
were doing before the arrival of the visitor
• remember the people’s clothing
• remember the people’s (and objects’) position in the room
• estimate the time since the guest’s last visit
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 6
Saccade MetricsSaccade Metrics
from Becker, 1991
approximately linearrelationship betweensaccade amplitude A andsaccade duration D:
dADD 0
20 ms < D0 < 30 ms2 ms/° < d < 3 ms/°
Example:for 20° saccade displayneeds to be changed~75ms after saccade onset
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 7
Anthropomorphic Robot HeadAnthropomorphic Robot Head
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 8
System overviewSystem overview
Gigabit Router
Desktop A Desktop B Desktop C
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 9
Motor SystemMotor System
• 9 DoF (hobby grade servo motors)• 2 Mini SSC II interface boards• Four bar linkage connection• Eye/neck system is redundant
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 10
Vision SystemVision System
• 2 Point Grey Research Firefly cameras (Firewire)• 640x480 resolution up to 30 fps• 2, 4, 6, and 8mm focal length lenses
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 11
Saccade Performance 1Saccade Performance 1
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 12
Saccade Performance 2Saccade Performance 2
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 14
Why Eye trackingWhy Eye tracking
Basic Neuroscience:- measuring brain output- understanding neural control architecture- psychophysics: how do we use gaze during natural tasks
Applications:- user interface design, human factors: e.g. eye tracking for driver of a car- advertising: do people look where I want them to look (in my web page, my newspaper ad, etc.)
Note 1: now several conferences solely devoted to thisNote 2: can also be done in fMRINote 3: possible in the real world: “portable eye trackers”
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 15
Eye tracking techniquesEye tracking techniques(Review in Duchowski&Vertegaal, 2000)
Contact lenses: with mirrors or induction loops- fast, accurate, uncomfortable (often used with bite bars)
Video based:- temporal accuracy limited to camera frame rate (60Hz)- less accurate (~1 deg)- typically with infrared illumination of the eye (dark pupil vs. bright pupil)- can be done remotely or camera can be attached to head
Electro-oculogram:- exploits electric dipole property of eye ball- fast but imprecise
Limbus tracking:- predecessor of the video based tracker- imprecise- small operating range
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 16
Electro-oculogramElectro-oculogram
•eye is electric dipole•electric field of moving dipole induces measurable voltages•provides analog voltage output that can be digitized and processed extremely fast, but technique is not accurate
electrode
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 17
Limbus TrackingLimbus Tracking
utilize difference in reflective properties of iris vs. sclera
infrared LED
photo diode
sclera
limbus
iris
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 18
Search CoilSearch Coil
gold standard for speed and accuracy (5-10’’), but quite uncomfortable and head movement restrained
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 19
Video based trackingVideo based tracking
most widely used today, good accuracy and speed, easy-to-use
dual purkinje trackerbright pupil image
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 20
inside of head mounted displayinside of head mounted display
U. of Rochester
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 21
Gaze contingent display changesGaze contingent display changes
Idea:decide what is being displayed contingent on where observer is looking
Saccade contingent updating (SCU):a special case of this: make display changes while a saccade is progressing(pioneering work by McConkie and colleagues)
• powerful technique for studying visual perception• frequently used in e.g. change blindness studies
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 22
Combination of video and limbus tracker Combination of video and limbus tracker inside HMD for gaze contingent displayinside HMD for gaze contingent display
analog limbustracker’ssensor with infrared LED,photo diodes(horizontal)
video based pupil tracker’s sensor
LCD displaysinside the HMD
• video based tracker for good accuracy• limbus tracker for low latency saccade detection
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 23
System OverviewSystem Overview
• 4 processor high-end graphics computer as backbone• images rendered in V8 helmet (Virtual Research)
Three sensors:• magnetic tracking device (Polhemus Fastrak)• limbus tracker (ASL 210), sampled at 1.25 kHz• pupil tracker (ASL 501), sampled at 60 Hz
Sensors send data via separate serial lines
Jochen Triesch, UC San Diego, http://cogsci.ucsd.edu/~triesch 24
Latency ComparisonLatency Comparison
in this example:limbus tracker has26 ms advantageover video tracker
on average: limbus tracker has 37±13 ms advantage (15 trials)
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