Saccadic Eye Movements

Question 1

What are saccades?

Answer 1

accurate, high velocity, non-ballistic

Question 2

What is the purpose of saccades?

Answer 2

to give samples of a scene

Question 3

How big is a saccade?

Answer 3

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

Question 4

What is the neurology of a saccade?

Answer 4

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

Question 5

Why do we need an efferent copy?

Answer 5

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

Question 6

Explain the controller signals for saccadic eye movements

Answer 6

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

Question 7

Describe eye position of a saccadic eye movement

Answer 7

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

Question 8

Describe the eye velocity of a saccadic eye movement

Answer 8

peak velocity is at 1/2 thru the eye movement

Question 9

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

Answer 9

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

Question 10

When is the active state tension highest?

Answer 10

at the end of the pulse signal

Question 11

What does a muscle force graph show for a saccade?

Answer 11

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

Question 12

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

Answer 12

the motor neurons

Question 13

Where are other neurons found that are involved in saccades?

Answer 13

in paramedian pontine reticular formation

Question 14

Where are tonic neurons found?

Answer 14

vestibular nucleus and nucleus prepositus

Question 15

Describe the action of pause neurons

Answer 15

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

Question 16

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

Answer 16

long lead and short lead

Question 17

What is a long lead?

Answer 17

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

Question 18

What is a short lead?

Answer 18

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

Question 19

Describe the action of a tonic neuron

Answer 19

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

Question 20

Describe the action of a motor neuron

Answer 20

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

Question 21

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

Answer 21

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

Question 22

What is a normometric saccade?

Answer 22

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

Question 23

What is a dysmetric saccade?

Answer 23

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

Question 24

What is a hypometric saccade?

Answer 24

dysmetric– too short

Question 25

What is a hypermetric saccade?

Answer 25

dysmetric-- too long, overshoot

Question 26

What is a pulseless saccade?

Answer 26

dysmetric-- pulse doesn't work

Question 27

What is a glissadic saccade?

Answer 27

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

Question 28

What are the three saccadic eye movement categories?

Answer 28

saccadic refixations, micro saccades, and saccadic oscillations and nystagmus

Question 29

What are the two saccadic refixations?

Answer 29

normometric and dysmetric

Question 30

What are the two normometric saccadic refixations?

Answer 30

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

Question 31

What are the two dysmetric saccadic refixations?

Answer 31

multistep and single step

Question 32

What are the three multistep dysmetric saccadic refixations?

Answer 32

corrective, closely spaced, and overlapping

Question 33

What are the two single step dysmetric saccadic refixations?

Answer 33

hypometric and hypermetric

Question 34

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

Answer 34

slow or pulseless saccade and glissadic undershoot

Question 35

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

Answer 35

glissadic overshoot and dynamic overshoot

Question 36

What are the clinical correlates of glissadic undershoot?

Answer 36

nerve or muscle paresis, fatigue, internuclear ophthalmoplegia, myasthenia

Question 37

What are the clinical correlates of pulseless saccadic refixations?

Answer 37

spinocerebellar degeneration

Question 38

What are the clinical correlates of glissadic overshoot?

Answer 38

abductor overshoot in internuclear ophthalmoplegia

Question 39

What are the clinical correlates of dynamic overshoot?

Answer 39

none

Question 40

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

Answer 40

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

Question 41

What are the clinical correlates of multistep saccadic refixations?

Answer 41

cerebellar disease, drug intoxication, fatigue, brainstem dysfunction

Question 42

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

Answer 42

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

Question 43

What is latency?

Answer 43

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

Question 44

What is the latency for saccades?

Answer 44

180-200 msec +/- 30 msec

Question 45

What actions make up the latency period for saccades?

Answer 45

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

Question 46

What is the latency and velocity for saccades?

Answer 46

200 msec latency and 1000 deg/sec

Question 47

What is the latency and velocity for a smooth pursuit?

Answer 47

125 msec and 50 deg/sec

Question 48

What is the latency and velocity for a VOR?

Answer 48

15 msec and 300 deg/sec

Question 49

What is the latency and velocity for vergence?

Answer 49

160 msec and 10 deg/sec

Question 50

What factors increase saccadic latency?

Answer 50

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

Question 51

What factors decrease saccadic latency?

Answer 51

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

Question 52

What are saccadic suppressions?

Answer 52

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

Question 53

What are saccadic omissions?

Answer 53

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

Question 54

What is best for visual masking?

Answer 54

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

Question 55

What is the absolute saccadic refractory period?

Answer 55

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

Question 56

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

Answer 56

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

Question 57

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

Answer 57

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

Question 58

T/F the bigger the saccade the faster it moves

Answer 58

true

Question 59

What is the result of frontal eye field damage?

Answer 59

impairment of saccadic motion of the side opposite the lesion

Question 60

What side do the eyes drift to with FEF damage?

Answer 60

eyes turn toward the side of the lesion

Question 61

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

Answer 61

head tilt the opposite direction of eye movement/damage

Question 62

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

Answer 62

true

Question 63

Why is neural inhibition important?

Answer 63

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

Question 64

What does Berthoz say about saccades?

Answer 64

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