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Ocular Motility > Saccadic Eye Movements > Flashcards

Saccadic Eye Movements Flashcards

1
Q

What are saccades?

A

accurate, high velocity, non-ballistic

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2
Q

What is the purpose of saccades?

A

to give samples of a scene

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3
Q

How big is a saccade?

A

less than 15 degrees, when larger involve the head and body

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4
Q

What is the neurology of a saccade?

A

saccade is generated by a pulse-step combo with an effect copy sent for a closed loop feedback system

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5
Q

Why do we need an efferent copy?

A

create a closed loop system, serves as comparator, tells perception that the world is stable

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6
Q

Explain the controller signals for saccadic eye movements

A

the agonist and antagonist pulses move in opposite directions and following Sherington’s law despite differences in power; step signal works to maintain the new position

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7
Q

Describe eye position of a saccadic eye movement

A

during pulse see the position change, during step eye held in the new position– made a 10 deg movement in the graph

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8
Q

Describe the eye velocity of a saccadic eye movement

A

peak velocity is at 1/2 thru the eye movement

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9
Q

Which has a faster velocity: short saccade or long saccade?

A

long saccades reach a faster velocity because it takes longer to reach the halfway point and they are able to reach a faster speed

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10
Q

When is the active state tension highest?

A

at the end of the pulse signal

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11
Q

What does a muscle force graph show for a saccade?

A

there is a spike for the pulse and then muscle forces drop to a lower baseline once step stabilizes the eye

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12
Q

What is found in the nucleus of a muscle performing an eye movement action?

A

the motor neurons

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13
Q

Where are other neurons found that are involved in saccades?

A

in paramedian pontine reticular formation

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14
Q

Where are tonic neurons found?

A

vestibular nucleus and nucleus prepositus

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15
Q

Describe the action of pause neurons

A

pause neurons function to keep the eyes stable, they signal at a constant rate the whole time except they shut off for the pulse signal

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16
Q

What two neural firing complexes are involved in the pulse signal?

A

long lead and short lead

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17
Q

What is a long lead?

A

The first part of the pulse signal, it’s firing rate begins to increase to signal a saccade

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18
Q

What is a short lead?

A

the second part of the pulse signal with a quick firing burst to signal a saccade

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19
Q

Describe the action of a tonic neuron

A

fires at a consistent pace until the movement then fires a bit more rapidly to maintain position after a step signal

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20
Q

Describe the action of a motor neuron

A

slow baseline, then fires to move muscle, then returns to a stable, yet higher baseline

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21
Q

What is different about neural firing when eyes are not starting in primary gaze?

A

neurons look different, elastic forces will return the eye to primary gaze instead of neurology

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22
Q

What is a normometric saccade?

A

aka orthometric, single saccade that lands appropriately on-target, normal gain and characteristics

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23
Q

What is a dysmetric saccade?

A

some problem with the gain or characteristics: hypometric, hypermetric, pulseless, glissadic

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24
Q

What is a hypometric saccade?

A

dysmetric– too short

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25
Q

What is a hypermetric saccade?

A

dysmetric– too long, overshoot

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26
Q

What is a pulseless saccade?

A

dysmetric– pulse doesn’t work

27
Q

What is a glissadic saccade?

A

dysmetric– pulse ok but not great, glides instead of jumps

28
Q

What are the three saccadic eye movement categories?

A

saccadic refixations, micro saccades, and saccadic oscillations and nystagmus

29
Q

What are the two saccadic refixations?

A

normometric and dysmetric

30
Q

What are the two normometric saccadic refixations?

A

main sequence saccade (majority) and low velocity long duration saccade (still end up at target)

31
Q

What are the two dysmetric saccadic refixations?

A

multistep and single step

32
Q

What are the three multistep dysmetric saccadic refixations?

A

corrective, closely spaced, and overlapping

33
Q

What are the two single step dysmetric saccadic refixations?

A

hypometric and hypermetric

34
Q

What are the two hypometric (undershoot) single step dysmetric saccadic refixations?

A

slow or pulseless saccade and glissadic undershoot

35
Q

What are the two hypermetric (overshoot) single step dysmetric saccadic refixations?

A

glissadic overshoot and dynamic overshoot

36
Q

What are the clinical correlates of glissadic undershoot?

A

nerve or muscle paresis, fatigue, internuclear ophthalmoplegia, myasthenia

37
Q

What are the clinical correlates of pulseless saccadic refixations?

A

spinocerebellar degeneration

38
Q

What are the clinical correlates of glissadic overshoot?

A

abductor overshoot in internuclear ophthalmoplegia

39
Q

What are the clinical correlates of dynamic overshoot?

A

none

40
Q

What are the clinical correlates of low velocity long duration saccadic refixations?

A

progressive supranuclear palsy, Wilson’s disease, Huntington’s chorea

41
Q

What are the clinical correlates of multistep saccadic refixations?

A

cerebellar disease, drug intoxication, fatigue, brainstem dysfunction

42
Q

What is the difference between old and young patients and their pursuits with catch up saccades?

A

older patients make more catch up saccades/sec while younger patients more appropriately calculate distance for better pursuit capability

43
Q

What is latency?

A

the amount of time between the decision to act and the actual movement starting aka reaction time

44
Q

What is the latency for saccades?

A

180-200 msec +/- 30 msec

45
Q

What actions make up the latency period for saccades?

A

neurosensory delay retina to cortex 50 msec; neuromotor delay w/ higher centers and midbrain 30 msec; computational delay 50 msec; cognitive decision making 50 msec

46
Q

What is the latency and velocity for saccades?

A

200 msec latency and 1000 deg/sec

47
Q

What is the latency and velocity for a smooth pursuit?

A

125 msec and 50 deg/sec

48
Q

What is the latency and velocity for a VOR?

A

15 msec and 300 deg/sec

49
Q

What is the latency and velocity for vergence?

A

160 msec and 10 deg/sec

50
Q

What factors increase saccadic latency?

A

very small and large target eccentricities, target uncertainty, increased target complexity, older age, inability to disengage, decreased motivation

51
Q

What factors decrease saccadic latency?

A

normal size eccentricities, target predictability, simple target, young age, uninteresting targets, increased motivation

52
Q

What are saccadic suppressions?

A

higher velocities (longer saccades), elevation of visual threshold, occurs during saccades and microsaccades, central neural inhibition

53
Q

What are saccadic omissions?

A

visual masking (forward of backward), primarily responsible for lack of gray out

54
Q

What is best for visual masking?

A

high contrast and contoured stimuli ex: looking between two faces the background is blurred

55
Q

What is the absolute saccadic refractory period?

A

the time the eyes are unable to generate a new saccade within the latency time, once program created motion is carried out

56
Q

What happens when a target is moved to a new position and back within the saccadic latency period of 200 msec?

A

the eye will move to the new location and remain there for the full 200 msec regardless of the duration of time the target actually stayed at the new position

57
Q

T/F if a new stimulus is shown within a very brief period, the first shift in position is often ignored

A

true, with a short time period in the new locations, the saccade is sometimes overridden (relative saccadic refractory period)

58
Q

T/F the bigger the saccade the faster it moves

A

true

59
Q

What is the result of frontal eye field damage?

A

impairment of saccadic motion of the side opposite the lesion

60
Q

What side do the eyes drift to with FEF damage?

A

eyes turn toward the side of the lesion

61
Q

What direction may a patient with FEF damage tilt their head?

A

head tilt the opposite direction of eye movement/damage

62
Q

T/F the sequence in which you take in information helps to build your perceptual representation of the scene

A

true

63
Q

Why is neural inhibition important?

A

it is a basic mechanism of production of movement and main mechanism of sensorimotor train ie inhibiting distractors and focusing on a task; it is also the source of perceptual mechanisms of filtering and selection and plays a decisive role in certain cognitive functions such as decision making

64
Q

What does Berthoz say about saccades?

A

saccades are a decision to act, not a response to a stimulus

Ocular Motility (13 decks)

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