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Control Of Human Movement > Eye Movement > Flashcards

Eye Movement Flashcards

1
Q

Why do we ‘move’ our eyes?

A

To bring points of interest over the fovea and to prevent blurring of the visual scene

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2
Q

What is a saccade?

A

A fast eye movement, that brings the area of interest onto the fovea (resetting of eye position during VOR and OKR)

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3
Q

What are the types of slow eye movements??

A 
Vestibulo-ocular reflex (VOR) - maintaining a stable image on the retina
Optokinetic reflex (OKR)

Smooth pursuit -tracks moving objects
Vergence - points the eyes in the same direction

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4
Q

Describe the 2 types of saccades

A

Reflex (stimulus driven)

Voluntary (no stimulus necessary)

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5
Q

Saccades are described as ballistic, what does this mean?

A

Upto 900deg/s, lasts 40-200ms (too fast for sensory feedback)

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6
Q

How is the observation of a scene characterised?

A

By alternating fixate and saccade patterns. These fixations last roughly 300ms

Vision is actively suppressed during a saccade

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7
Q

What is a corrective saccade?

A

Normal saccadic eye movements are often characterised by a slight undershooting followed by a corrective saccade

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8
Q

What is a dysmetric saccade?

A

The cerebellum is important in tuning the gain of saccadic eye movements. Dysmetric saccades cause visual problems in cerebellar patients

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9
Q

What does hypermetric and hypometric mean?

A

Hypermetric - a saccade that overshoots it’s target

Hypometric - a saccade that falls short of it intended goal

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10
Q

Discuss the vestibular system in terms of its components?

A

Has 3 semicircular canals that detect head rotation and 2 otolith organs that detect tilt (gravity) and linear acceleration

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11
Q

How does the VOR help to stabilise the visual image?

A

Rotates the eyes to compensate for head movement, which helps to stabilise the visual image

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12
Q

Is the VOR fast??

A

Yes, it is a basic brainstem circuit with only 3 neurons, therefore is extremely fast (~15ms from head to eye movement)

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13
Q

How is VOR function tested??

A

Rotation in darkness is used to test VOR function, which produces an alternating pattern of fast and slow eye movements called nystagmus

Quick phase (saccades) resets the position of the eye in the head

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14
Q

What should happen if the VOR is working perfectly when tested??

A

If the VOR is working perfectly, the slow phase eye rotation and head rotation should cancel out. This equates to a gain of 1. VOR gain may be less than 1 if the vestibular apparatus is damaged.

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15
Q

What are examples of VOR adaptation?

A

The rotating chair and curtain

Also if you get a stronger pair of glasses, you need to adapt your VOR

Cerebellar disease impairs VOR adaptation

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16
Q

What does a different relationship between head and scene movement require??

A

Different VOR gain

17
Q

what can comprise the VOR?

A

Anything which affects vestibular function

18
Q

Describe vestibular loss??

A

Could be many things including:

Viral infection, head injury, surgical intervention. Symptoms include balance loss, disorientation and oscillopsia (blurring of visual field, essentially absent VOR)

19
Q

Describe ageing in terms of VOR?

A

Vestibular hair cells are gradually lost with age

20
Q

Discuss alcohol and the VOR?

A

Alcohol nystagmus is caused by changes in specific gravity of the fluid in the canals

21
Q

What is the vestibular storage mechanism?

A

During continuous rotation, the vestibular signal decays much earlier than the eye movement (6 seconds rather than 15 seconds)

The brainstem has a velocity storage mechanism to prolong gaze stabilisation

22
Q

What happens to the vestibular storage mechanism during prolonged rotation?

A

The signal fails - this is when the optokinetic reflex takes over (assuming vision is available)

23
Q

What is OKR and what type of movements is it better for??

A

OKR performs a similar function to the VOR but is visually driven

Better for low frequency movements , whereas the VOR is adapted to high frequency

24
Q

What must smooth pursuit involve??

A

Must involve prediction, as visual feedback is too slow. Hence the brain must predict the future flight of the object, eyes will continue moving after the object disappears.

25
Q

What are the 4 methods of eye tracking?

A

Scleral coil
Infrared reflectance
Electro-oculography (EOG)
Video-oculography (VOG)

26
Q

What is a scleral coil?

A

Contact lens with embedded wire coils
Provides accurate eye position in all 3 axes (Yaw, pitch and roll)
However, is very invasive and uncomfortable (wire can scratch cornea)

27
Q

What is infrared reflectance?

A

A beam of infrared reflected from the cornea
As the eye rotates, the beam is reflected in a different direction. This change in position is detected by the IR detector.
Can be used in the dark

28
Q

How does EOG work ?

A

The retina produces measurable electric charge as there is a permanent potential difference between the cornea and retina which sets up an electrical field in the surrounding tissue that can be measured.

29
Q

What does EOG do?

A

Measures horizontal and vertical eye movement
Commonly used in neurology clinics to test VOR function
Works with the eyes closed and can provide gaze information if head is stationary

30
Q

Discuss VOG and gaze tracking?

A

Simultaneous recording of the eye and scene allows point of gaze to be tracked

31
Q

What did Land (2006) find when looking at eye movements?

A

Found eye movements tend to precede object manipulation by ~0.6s, moving onto the next object ~0.6 seconds before the action is completed

32
Q

Discuss gaze position during locomotion.

A

When walking in difficult terrain, gaze typically stays 2 steps ahead.
Roughly 2 fixations per step, hence foot placement is generally planned and 2 steps in advance.

33
Q

What did Young and Hollands (2010) find about gaze and locomotion?

A

Older adults tend to show more predictive sampling, at the expense of the current step

34
Q

Discuss batmens gaze during cricket?

A

Must predict the location of the bounce to successfully strike the ball
Their eye movements monitor the moment when the ball is released, make a predictive saccade to the place where they expect it to hit the ground , wait for it to bounce and follow its trajectory for 100-200ms after the bounce

35
Q

What are the differences between poor and skilled batsmen?

A
  • downward saccade occurs much earlier in better batsmen (0.14-0.2s)
  • poor batsmen show a weaker coupling between timing of eye movement and bounce
  • skilled players make more use of information before ball is released (yarrow et al,2009)
36
Q

What is action observation?

A

When observing movement, gaze is predictive not reactive . Which mimics the gaze pattern observed when actually moving

Control Of Human Movement (15 decks)

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