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Ocular Motility > Pursuit Eye Movements > Flashcards

Pursuit Eye Movements Flashcards

1
Q

Ocular pursuit of the eye appeared late in the course of evolution and followed appearance of ___ which exists in primates (and reptiles)

A

the fovea

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2
Q

Which species have two fovea?

A

birds

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3
Q

Which species have an area centralis with more cones but more rods overall

A

cats/dogs (night vision)

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4
Q

T/F we can track an object without a fovea

A

false

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5
Q

How do species without a fovea track movement?

A

saccades

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6
Q

What is the negative feedback in pursuits?

A

inhibitory closed loop, uses image motion as central command to efferent pathway

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7
Q

T/F pursuits can modify themselves while movement is still going on

A

true

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8
Q

Which has more complex neurology, pursuits or saccades?

A

pursuits

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9
Q

How does negative pursuit feedback correct for too fast or too slow?

A

too fast– slow eye movement, too slow–put in corrective saccade to keep up

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10
Q

How does the visual system know if the pursuit is accurate?

A

compare target motion and image motion on the retina

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11
Q

What are the solid and dashed lines on the pursuit model diagram?

A

solid–flow of neural signals

dashed–physical events

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12
Q

What is the positive feedback in pursuits?

A

eye velocity; helps get a sense of the degree of error

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13
Q

Where does the afferent pathway info go?

A

summative area, like neural integrator

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14
Q

When does the efferent pathway of a pursuit begin?

A

once target velocity has been reconstructed following eye velocity positive feedback

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15
Q

When does pursuit command happen?

A

After positive feedback and efferent pathway

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16
Q

What are the 3 afferent pathways?

A

retinal acceleration error, retinal velocity error, and retinal position error

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17
Q

How long is the delay between target motion and afferent pathways?

A

90 msec

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18
Q

T/F afferent pathways need to be summed before going to efferent pathways?

A

true

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19
Q

As target velocity increases, pursuit gain…

A

decreases; especially in older population

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20
Q

Where do young people start to see a decrease in pursuit gain?

A

40-50 deg/sec drops to gain of .9-.8

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21
Q

When do older people decrease pursuit gain to 0.8

A

target velocity of 10 deg/sec

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22
Q

What is pursuit latency?

A

time take from the decision to move to the beginning of the actual movement

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23
Q

What is pursuit latency for fast targets?

A

100 milliseconds +/- 5 msec

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24
Q

What is pursuit latency for slow targets (less than 5 degrees per second)?

A

up to 125 msec

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25
Q

In general, the slower the pursuit, the longer the…

A

latency

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26
Q

Rank the latency of eye movements from lowest to highest

A

VOR, pursuit, vergence, saccades

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27
Q

Rank the velocity of eye movements from fastest to slowest

A

saccades, VOR, pursuit, vergence

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28
Q

What is the latency of a smooth pursuit?

A

100-125 msec

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29
Q

What is the velocity of a pursuit?

A

80 deg/sec

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30
Q

What is the latency of a saccade?

A

200 msec

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31
Q

What is the velocity of a saccade?

A

1000 deg/sec

32
Q

What is the velocity of VOR?

A

300 deg/sec

33
Q

What is the latency of VOR?

A

15 msec

34
Q

What is the latency of vergence?

A

160 msec

35
Q

What is the velocity of vergence?

A

10 deg/sec

36
Q

How long can eye velocity match stimulus velocity?

A

to 80 deg/sec

37
Q

Gaze orientation was one of the first functions that required the development of a brain that could…

A

predict, be curious, and simulate action

38
Q

What two things allow for pursuits?

A

cortical development and precise foveal function

39
Q

What is taxis?

A

orientation towards a sensory source ex: phototaxis, heliotaxis, thermotaxis, etc

40
Q

What four things does gaze orientation encompass?

A

projection, questioning, visualization, and prediction

41
Q

Berthoz says gaze orientation is

A

stationary locomotion

42
Q

What are the two frames of reference?

A

egocentric and allocentric

43
Q

What is egocentric?

A

reference is relative to self

44
Q

What is allocentric?

A

reference is relative to objects in the environment

45
Q

Which frame of reference develops first?

A

egocentric

46
Q

How does a baby direct its gaze?

A

using the body and turning head and eyes about its body axis

47
Q

Before 18 months babies fixate on

A

a landmark to which they anchor their progression around the room

48
Q

What is the first sign a baby is constructing allocentric relationships?

A

locating an object in the environment

49
Q

What happens if an baby’s anchor point is hidden?

A

reverts back to egocentric strategy

50
Q

After 18 months an infant can…

A

mentally update his position in the room while he is walking, employing mechanism of mental rotation and translation

51
Q

T/F the intervention of high-level cognitive mechanisms in adaptation to sensory conflicts is really a problem of frames of reference

A

true

52
Q

What is one of the most important aspects of adaptation?

A

ability to move from one frame of reference to another and to combine them

53
Q

What do patients need to relearn after VOR lesion?

A

how to move from one frame of reference to another

54
Q

What is maximum eye velocity for pursuits?

A

80 degrees/sec

55
Q

What happens if target motion is faster than 80 degrees/sec?

A

need saccades to get back on target; older=more catch-up saccades

56
Q

What is natures way around the slowness of pursuits?

A

prediction

57
Q

Why is batter unable to maintain tracing when ball is at close distance?

A

high angular velocity

58
Q

The faster the pitch…

A

the farther away from home plate your eyes can accurately track the ball

59
Q

What are 3 strategies batters use to track a ball?

A

track w/ eye movements only and fall behind the last 10 feet; track with head movements and pursuits and fall behind in last 5 feet; use pursuits, then saccade to predicted point, continue to follow with peripheral vision, and resume smooth pursuit tracking at end with ball’s image on fovea

60
Q

T/F batters use vergence eye movements

A

false

61
Q

Describe the flight of the baseball in thirds

A

1/3 batter forms mental model of trajectory, 2/3 observe difference b/w actual and mental, update mental and finalize swing, 3/3 observe errors in mental model to better track the next pitch

62
Q

Superstars have success because:

A

faster pursuit, ability to suppress VOR, anticipatory saccades, prediction

63
Q

How do we quantify quickness?

A

latency of saccadic eye movement system and eye-hand reaction time– lab only not clinic

64
Q

What is zero-latency tracking?

A

overcoming time delay and tracking predictable targets with no delay provided the target position waveform is smooth and predictable with frequency b/w 0.1 and 1.0 Hz with small accelerations

65
Q

What does the time to collision concept relate

A

T=relation b/w observed diameter of the car in front which you are approaching and the speed with which this diameter expands

66
Q

If movement proceeds at constant velocity, time to collision can be evaluated by…

A

speed with which the retinal image of the object expands

67
Q

Time to contact is given solely by…

A

retinal cues

68
Q

How does our hand adapt its shape to the apparent shape of an object before contact?

A

we sample, calculate, and open change then change shape without conscious thought

69
Q

T/F the muscular activity of the arm is always initiated at the same time (before contact), no matter what the velocity of the target

A

true

70
Q

T/F the hand always take the shape of the object we are about to catch at the same distance from the hand

A

false– just happens at the same time before catching no at the same distance from the hand

71
Q

How does tennis relate to time to collision?

A

the movement of the racket is constant and independent of the approach velocity, thus the beginning of the movement may in fact be adjusted by the value of the T margin– adjust based on calculation of retinal slip made internally

72
Q

How much time is needed to estimate distance/time to contact?

A

need 240-300 msec to catch a ball

73
Q

To catch a ball traveling at 10 meters per second, the athlete has a temporal window of ___ during which his hand can remain closed

A

50 msec

74
Q

Catching a ball is preceded by __ that prepares for impact and is followed by a ___ induced by the impact

A

anticipatory muscular activity, reflex activity

75
Q

Subjects seem to base their response, whether anticipation or reflex on…

A

prediction of the dynamic properties of the ball under the influence of gravity

Ocular Motility (13 decks)

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