Ocular Motility: Lecture 7: Saccadic Eye movements 1

Question 1

Control Systems Theory

1. It’s the arrangement of physical components connected in such a manner as to do what 3 things?
2. I = input: Which does what?
3. T (Transfer function) which does what?
4. Examples of physical Systems?

Answer 1

1. Command, Direct or regulate itself
2. goes into the system then transforms the input into the output
3. math representation of mechanisms that transform the input into the output
4. Electric Switch, Thermostat Furnace, and Toaster

Question 2

Electric Switch…

1. Input = ?
2. Output = ?
3. Whatever goes in, goes out…so?

Answer 2

1. Input current/voltage
2. output current/voltage
3. So no real transformation

Question 3

Thermostat furnace

1. Input
2. Output?

Answer 3

1. Setting on thermostat (reference temperature)

2. Heat generated by furnace

Question 4

In oculomotor system (Smoot Pursuit)

1. Input = ?
2. Output = ?

Answer 4

1. Visual stimulus (moving stimulus)

2. eye movement following the object

Question 5

In oculomotor system (VOR)

1. Input = ?
2. Output = ?
3. Visual input goes to what?
4. Brain transforms it: resulting in what?

Answer 5

1. Head Rotation
2. VOR Eye Movement
3. Goes to Black box representing Oculomotor Brain
4. in an eye movement

Question 6

Control System

1 This system runs until what?

Answer 6

1. until the Output matches the Input

Question 7

Why do we need saccades?

1. They’re Fast Conjugate Eye Movements that move both eyes how?
2. Responsible for Resetting the Eyes back to what position? During what 2 things?
3. Need to be fast to get the eyes on the target when?

Answer 7

1. Quickly in the Same direction
2. back to the Mid-Orbital Position; During Vestibulo-ocular or Optokinetic Stimulation
3. ASAP and to minimize blurirng

Question 8

Overview of Saccades

1. Most of the Saccades are how many degrees in Amplitude?
   a. During a saccade, a Neural signal called what is generated?
2. A PRIMARY SACCADE that has nearly normal gain and slightly reduced may be a normal strategy adopted by what system?
3. Visual Acuity is less than what?

Answer 8

1. 15 degrees in amplitude
   a. Called EFFERENCE COPY
2. by the Saccade System
3. less than 20/1000

Question 9

Saccadic Eye Movement

1. How fast of an eye movement is it?
   a. It’s the fastest what?
2. Can be made toward what 2 types of stimuli?
3. Saccade speed is not under Voluntary control, but depends on what?
4. Can get to any position in VF using saccadic Eye movement (What 4)?

Answer 9

1. Very Rapid eye movement.
   a. Fastest skeletal movement that we’re capable of
2. Auditory and Tactile stimuli
3. on the Size of the movement
4. Up, Down, Horizontally, and Obliquely

Question 10

Saccadic Latency

1. Refers to the time from onset of the nonpredictable step of target movement to onset of what?
   a. It’s about what time with a standard deviation of what?
2. Afferent or Visual Neurosensory delay of what?
3. Efferent of Neuromotor delay of what?
4. Computational Delay = ?
5. Decision making delay = ?

Answer 10

1. of the Saccadic Eye movement initiated to Foveate the Displaced Target
   a. about 180-200 msec w/a standard deviation of 30 msec
2. 50 msec
3. 30 msec
4. 50 msec
5. 50 msec

Question 11

Factors that Affect Saccadic Latency

1. 4 things that decrease it? (FITH)

(6 increase it…)

Answer 11

1. a. Forewarning Period
   b. Increased Target Luminance or Contrast
   c. Target Predictability
   d. Heightened Attention

Question 12

Saccadic Velocity and Duration

1. In normal subjects, peak velocity of saccades varies from what 2 degrees/sec?
   a. for Amplitude ranging from what degrees?
2. The Larger saccades, what happens to the Peak Velocity?
   a. The relationship b/w Saccade Amplitude and Peak Velocity has been called what?
3. The duration of saccades is approximately linearly related to what?
   a. It varies 30-100 msec for amplitude ranging from what degrees?

Answer 12

1. 30-700 deg/sec
   a. for amp ranging from 0.5 to 40 degrees
2. The HIGHER the Peak Velocity
   a. the MAIN SEQUENCE
3. to the Amplitude
   a. from 0.5-40 degrees

Question 13

Main Sequence

1. Duration-Amplitude Curve: Relationship B/w Duration and Amplitude is what?
   a. Small Amplitude Saccades are what?
2. Velocity-Amplitude Curve:
   a. PEAK VELOCITY of Saccade Vs. Amplitude, and what kind of relationship is it?
   b. The curve is often called a what?
3. the MAIN SEQUENCE Relationship reflects what?

Answer 13

1. is LINEAR
   a. are Over Quickly
2. a. it’s an Exponential relationship
   b. a MAIN SEQUENCE
3. the Pulse component of the Pulse-Step Neurologic Controller signal for Saccades

Question 14

Saccade Dynamics

1. The Largest Commonly made saccades have what deg of amplitudes and what duration time?
2. If saccades are SLUGGISH, their main sequence values will be what?
3. What factors reduce Peak Saccadic Velocity? (6: FANG DD)

Answer 14

1. 15 degree amplitudes and 50 msec durations
2. They’ll be low for the amplitude of the resulting saccade
3. Fatigue; Age; Neurologic Diseases; Gaze Angle; Darkness and Drugs that reduce alertness

Question 15

Pulse-Step Innervation for Saccadic Eye Movement

1. It consists of what?
2. Phasic contraction of the Agonist Muscle overcomes what?
3. The Saccadic Step is what?
   a. It’s created from what?

Answer 15

1. of a High-frequency burst of Phasic Activity in Agonist Motoneurons
2. the Viscous Drag in the Orbit and is responsible for the Rapid Eye Movement
3. an Eye Position Command
   a. the Pulse (an eye velocity command) by a neural network that integrates, conjugate eye-velocity commands into the appropriate position-coded info for the ocular motoneurons

Question 16

Pulse-Step Innervation for Saccadic Eye Movement

1. For horizontal movements, the neural integrator Consists of what Nuclei?
2. For Vertical and Torsional Movements, the Neural Integrator is in what?

Answer 16

1. Medial vestibular Nucleus and Adjacent Nucleus Prepositus Hypoglossi in the Medulla
2. Interstitial Nucleus of Cajal in the Midbrain

Question 17

Saccadic Eye Movement

1. Normometric Saccade: What is it?
   a. The underlying signal consists of what?
2. Dysmetric Saccades can be what type of step movements?
   a. They can also be what?
3. Hypometric Saccades can initially do what?
4. Hypermetric Saccades can initially do what?

Answer 17

1. A Single, Accurate movement having approximate gain and dynamics
   a. of a Single, precise matched pulse-step combination
2. either single-step or multiple-step movements.
   a. too small or too large (hypermetric) w/respect to the intended target position
3. Undershoot the target in a variety of ways
4. Overshoot the target in a variety of ways

Question 18

Disorders of Saccadic Pulse and Step

1. Hypometric Saccade: Pulse magnitude (width X height) is what?
2. Slow Saccade decreased pulse height with what 2 things?
3. Gaze evoked Nystagmus: 2 things?

Answer 18

1. too small, but pulse and step are matched appropriately
2. with normal pulse amplitude and normal pulse-step match
3. Normal Pulse and Poorly Sustained Step

Question 19

Sample Data System

1. What is it?
2. What did they find the eye would do after the normal latency period?

Answer 19

1. no info being fed b/w data sample readings
2. the eye saccaded by an amt equal to the pulse amplitude and then remained in that position for 200 msec before shifting back to the original (discrete or periodic motor sampling of visual information)

Question 20

Ballistic Nature of Saccades

1. Saccades have been referred to as a Ballistic. Why?
2. Predication?
3. Without Prediction?
   * Interval b/w saccades was independent of the interval b/w the target jumps away and back to the fovea. What does this suggest?

Answer 20

1. their force program of pulse and step appeared to be preprogrammed one latency period prior to the response
2. Typical saccade latency of 200 msec can be reduced by prediction
3. saccade dysmetria and over-and under-shoots occur.
   * that the saccadic system could only react to 1 target at a time and there was a fixed latency or refractory period, during which a second saccade couldn’t be started after the first.

Question 21

Saccadic Prediction and Accuracy

1. Prediction is ESSENTIAL for what?
2. Prediction also occurs when the motion of the eye is very repetitive and synchronized with motion of a what?
3. Large Saccades usually fall short of their target and are followed up with a series of what?
4. Individuals of all ages and backgrounds demonstrate prediction, usually w/in what?
5. Process Likely PERFORMED by what?

Answer 21

1. for almost all motor systems that control balance and locomotion
2. of a highly repetitive target
3. of smaller corrective saccades
4. w/in 5 cycles or so of repetitive target motion
5. CEREBELLUM

Question 22

Saccadic Suppression and Omission

1. Suppression: Detection of a BRIEF FLASH OF LIGHT decreases by what % or more in how much time?
   a. AKA?
2. Omission: Masking refers to the obscuration of a target by either an immediately preceding or a succeeding visual stimulus, especially at what?
3. a 1-5 msec flash presented during a 50-70 msec saccade produced what?

Answer 22

1. 50% 20msec before to approximately 35 msec after a saccade
   a. CENTRAL NEURAL INHIBITION
2. at High Contrast Levels and in the Presence of a Full Array of Contours
3. a Clear Percept of the otherwise darkened room

Question 23

Saccadic Omission and Generation

1. Extension of the flash duration, either before the saccade or after the SACCADE was completed, however produced what?
2. A Flash presented during the entire Saccade Excursion (50-70 msec) resulted in what?
3. Visual Masking is the PRIMARY FACTOR Contributing to the Absence of what?
4. VA during the SACCADE is POORER than what?

Answer 23

1. a Clear Percept
2. in a Very Smeared, Grayish percept of the otherwise darkened room
3. of Perceived “Gray-out” During saccades
4. poorer than 20/1000

Question 24

Transient Vergence During Saccades

1. During Horizontal Saccades, there’s a dynamic Divergence of up to what?
   a. Saccades in the Abducting Eye have SLIGHTLY GREATER what?
2. During Vertical Saccades, there are transient changed in Horizontal Vergence (how much) with divergence in what? and Convergence in what?
3. Vertical Vergence during Vertical saccades are what?

Answer 24

1. 3 degrees
   a. AMPLITUDE AND PEAK VELOCITY AND SHORTER DURATION
2. 4 degrees; Upward gaze; Downward Gaze
3. are Considerably Smaller

Question 25

Aging and Saccades

1. Systemic Increase in Latency with age in Adults: How much?
2. Peak Saccadic Velocity has also shown to decrease with age: how much?

Answer 25

1. 1-2 msec per year

2. 1 deg per sec per year

Question 26

Saccadic Adaptation

1. Normal Self correcting rapid dynamic changes in effective calibration of the saccadic eye movement system that reduce the probability of occurrence of what?
2. ADAPTATION MAY OCCUR AFTER AS FEW AS how many saccades?

Answer 26

1. of an Inaccurate Saccade

2. as 70 saccades