Medical Electronics - Oculography · 2012. 10. 30. · Electro-Oculography (EOG) •~50 years old •Measurement of skin’s electric potential differences from electrodes placed

Politechnika Łódzka, ul. Żeromskiego 116, 90-924 Łódź, tel. (042) 631 28 83

www.kapitalludzki.p.lodz.pl

„Innowacyjna dydaktyka bez ograniczeń - zintegrowany

rozwój Politechniki Łódzkiej - zarządzanie Uczelnią,

nowoczesna oferta edukacyjna i wzmacniania zdolności

do zatrudniania osób niepełnosprawnych”

Prezentacja multimedialna współfinansowana przez

Unię Europejską w ramach

Europejskiego Funduszu Społecznego w projekcie pt.

„Medical Electronics - Oculography”

Projekt współfinansowany przez Unię Europejską

w ramach Europejskiego Funduszu Społecznego

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Why is eye-tracking important?

• We focus our gaze on the object or region of

interest

Tracking eye movements

=

Follow along the path of attention

• Get information about:

– What draws person’s attention

– How does the person

percieve the scene

Medical Electronics 2



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Eye Movements

• Eyes move all the time (even during sleep)

• 6 degrees of freedom

• movement controlled by 3 pairs of extrinsic muscles

Muscle Action

Superior rectus Eye looks up

Inferior rectus Eye looks down

Lateral rectus Eye rotates laterally

Medial rectus Eye rotates medially

Superior oblique Eye rolls, looks down and to

the side

Inferior oblique Eye rolls, looks up and to

the side

Medical Electronics



Eye movements




Eye movements




Eye movements

• Several different movement types, such as – Smooth pursuit

– Vestibular ocular reflex

– Optokinesis

– Vergence

• But the most interesting types are – Fixation

– Saccade




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Fixations

• Eye is a (relatively) still and “fixated” to the certain

point. e.g. reading a single word.

• All the information from the scene is (mainly)

acquired during fixation.

• Duration varies from 120-1000 ms, typically

200-600 ms.

• Typical fixation frequency is < 3 Hz

• Interspersed with saccades

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Fixations

• Even when fixed, eyes exhibit involuntary movements:

– Tremos

• small tremors (tremblings) of eyes at 30-80Hz

– Slow drifts

• drifting movements of the eyes = even if an object is stationary, the image drifts

across the fovea.

– Flicking

• as the image drifts to the edge of the fovea, the involuntary mechanism causes

a reflex flicking of the eyeball so that the image is once again projected onto the

fovea.

• The drifting movements and flicking movements are in opposite

directions.




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Saccades

• “Jumps” which connect fixations

• Very rapid - duration is typically only 40-120 ms

• Very fast (up to 600 o/s) and therefore the vision

system is suppressed during the movement

• Saccades are used to move the fixation point

– If larger than 30 degree movement is required, head

moves along with eyes

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Fixations and saccades


http://en.wikipedia.org/



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Visual attention

• We must attend to something when acting on the

basis of visual input

• Defines:

– „where”

– „what”

• The perception of a complex scene involves a

complicated pattern of fixations and saccades

• Gaze path depends mainly on „what”



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Gaze path - example


http://www.diku.dk/



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Free examination


http://www.diku.dk/



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Material circumstances


http://www.diku.dk/

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How old are they?


http://www.diku.dk/

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What were they doing?


http://www.diku.dk/

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Clothes


http://www.diku.dk/

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Positions


http://www.diku.dk/

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When did they meet before?


http://www.diku.dk/

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Eyetracking - history

• Research since 1850s

• First attempts – direct observation

• XXc – use of oculographs:

– mechanical

– electrical

– photoelectrical

– magnetoelectrical

– video




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First video-based eye tracking


Hunziker (1970):

8 mm film

+

glass plate




22 Photo-Oculography (POG)

and Video-Oculography (VOG)

• Tracking eye movements by the digital processing

of video images of the eyes

• Different features used:

– Pupil shape

– Iris-sclera boundary

– Corneal reflection

of the light source

• Often employs IR illumination

• Requires fixed head position


http://www.archimuse.com

Medical Electronics



Video-based eyetracking

– Head-mounted devices

– Non-contact devices

– Wereable devices




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Video-based eyetracking


www.jneuroengrehab.com

http://work.thaslwanter.at

Medical Electronics



Tobii eye-trackers




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Video-Based Pupil/Corneal Reflection

• Measuring corneal reflections relative to the

locationof the pupil center

• Corneal reflections = Purkinje reflections =

Purkinje images

– 1st – from front surface of the cornea

– 2nd – from rear surface of the cornea

– 3rd – from front surface of the lens

– 4th – from rear surface of the lens

• Point of Regard estimation requires 1st and 4th

Purkinje images

Medical Electronics 26 Medical Electronics



Purkinje reflections


Ray of light



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Video-Based Pupil/Corneal Reflection


http://people.usd.edu

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Dual Purkinje eye-tracker

http://www.fourward.com

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Ober Consulting

http://www.ober-consulting.com/

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Scleral Contact Lens/Search Coil

• Most precise method

• Contact lens of relatively large diameter with a

mounted stalk:

– Reflecting phosphors

– Line diagrams

– Wire coils

• Typically search coil embedded in contact lens +

electromagnetic field frame




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http://www.skalar.nl

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http://www.skalar.nl

http://mvl.mit.edu

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Electro-Oculography (EOG)

• ~50 years old

• Measurement of skin’s electric potential

differences from electrodes placed around the

eyes

• Range of potentials:15-2000μV, in practice 0.4 – 1mV

• Eye movements relative to head position

– ±70°, where 0° is in front and ± 90° directly

vertical/lateral to the eyes

• Not suitable for Point of Regard measurements




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Electro-Oculography (EOG)


http://www.human-factors-consult.de



EOG – electrode placement


Vertical

Movements

(CH1)

Horizontal

Movements

(CH2)

Ground



Example electrooculogram


http://www.hindawi.com













EOG

• Application

– Diagnosis of organic changes in retina

– Toxic damage of retina

– Degenerative and vascular diseases of retina

– Addition to electroretinography

• Procedure

– Carried out in the dark

– Time - few to tens of minutes

– Measure „swinging” movements of the eyes in the range of ~40 degrees,

i.e. look at two sides of the illuminated table

– Recording has sinusoidal shape

– Results presented n terms of Arden ratio

• ISCEV Standard for Clinical Electro-oculography (first issued 1993 –

reapproved 1998)





ISCEV Standard for Clinical Electro-oculography (EOG)

2006

eog.pdf



Electrooculographs


Digital electroretinograph

and electrooculograph

(with evoked potential)

EP-1000 PRO

Messbrille

ETH Zurich

Wearable Eye Tracker



Make EOG by yourself

• http://community.curuxa.org/en/Electrooculograph

• http://makeprojects.com/Project/Eyeboard+Electrooculography+(EOG)

+System/1686/1#.UIByusVLNLE


http://community.curuxa.org/en/Electrooculograph

http://makeprojects.com/Project/Eyeboard+Electrooculography+(EOG)+System/1686/1

http://makeprojects.com/Project/Eyeboard+Electrooculography+(EOG)+System/1686/1



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Eye tracking - what is it for?

• Medical research

• In-vehicle research

• Web usability

• Advertising

• Marketing

• Communication systems for disabled

• …




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In-vehicle research





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Web usability

http://www.seomoz.org/

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Web usability

http://www.seotops.com/

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Advertising

http://www.visiontrackresearch.com/

Medical Electronics

Politechnika Łódzka, ul. Żeromskiego 116, 90-924 Łódź, tel. (042) 631 28 83

www.kapitalludzki.p.lodz.pl

„Innowacyjna dydaktyka bez ograniczeń - zintegrowany

rozwój Politechniki Łódzkiej - zarządzanie Uczelnią,

nowoczesna oferta edukacyjna i wzmacniania zdolności

do zatrudniania osób niepełnosprawnych”

Prezentacja multimedialna współfinansowana przez

Unię Europejską w ramach

Europejskiego Funduszu Społecznego w projekcie pt.

„ Medical Electronics - EOG”

Documents

Medical Electronics - Oculography · 2012. 10. 30. · Electro-Oculography (EOG) •~50 years old •Measurement of skin’s electric potential differences from electrodes placed