Saccadic Eye Movement

Question 1

Most saccades made are less than __ degrees. Quick, no body movement required. ___ degrees requires whole body movement.

Answer 1

15 degrees.

20-30 degrees

Question 2

Saccade is generated by what?

Answer 2

Pulse, step combo. Efferent copy also sent. Serves as a comparison. Taels perception that the world is stable.

Question 3

Long vs short saccade. Which one is faster?

Answer 3

Longer the saccade, faster the movement.

Question 4

Peak velocity of saccade is where

Answer 4

Is located half way through the saccade.

Question 5

What things happen when you move away from primary gaze?

Answer 5

Pause neuron must stop firing.
Burst neurons (long and short lead) help give pulse signal. They fire a lot before the beginning of the movement.
Tonic neurons begin to fire a little more rapidly once at the new position. Maintain the step signal.
Motor neuron is final step. It is found in the appropriate nucleus associated with the muscle performing the action.

Question 6

Tonic neurons are mostly found in the ___ and ____

Other neurons are in the paramedic pontine reticular formation.

Answer 6

Vestibular nucleus and nucleus prepositus.

Question 7

Normometric/Orthometric

Answer 7

Normal. Single saccade that lands appropriately on target. Normal gain and characteristics.

Question 8

Dysmetric - what are the 4 ways to describe an abnormal saccade?

Answer 8

Abnormal saccade. Some problem with the gain (1 and 2) or characteristics (3 and 4).

1. Hypometric. Undershoot.
2. Hypermetric. Overshoot
3. Pulseless. Pulse signal not working.
4. Glissadic. Presents as aglide movement. Poor pulse.

Question 9

2 examples of Single step hypsometric saccade problem? 2 examples of single step hyper metric saccade problem?

Answer 9

Hypo pulseless or hypo glissadic

Hyper Glissadic or hyper dynamic (must make another saccade to correct)

Question 10

Saccades and age

Answer 10

For a given target velocity, older patients must make more catch u saccades within each pursuit. You should slow test down for older patients.

For younger patients, they make less catch up saccades because they more appropriately calculate the distance and have better pursuit capability.

Question 11

Latency

Answer 11

The amount of time between the decision to act and the actual movement starting. For saccades, approx 180-200 ms. Many factors can affect latency, such as disease.

Question 12

Latency in msec and velocity in deg/sec for

1. Saccades
2. Smooth pursuit
3. Vestibulo ocular reflex
4. Vergence

Answer 12

1. 200 ms latency. 1000 degree/sec.
2. 125 ms latency. 50 degree per sec
3. 15 ms latency. 300 degree per sec.
4. 160 ms latency. 10 degree per sec.

Take away: VOR latency period is very short. Vergence latency is relatively long compared to the short velocity it moves.

Question 13

What factors increase saccadic latency?

Answer 13

Latency time will increase for:
very short or large eccentricities.
Target uncertainty
Increased target complexity
Older subject
Inability to disengage attention. Hooked onto object.
Decreased motivation/not interested in surround.

Question 14

What factors decrease saccadic latency?

Answer 14

Latency time will decrease for:
Normal eccentricity
Target predictability 
Simple target
Younger subject
Uninteresting target. Ready to move on. 
Increased motivation to gather more information about surround.

Question 15

Why does suppression occur during saccades and microsaccades?

Answer 15

Central neural inhibitors. Prevents blur of images when moving from point A to point B. Typically during longer saccades.

Question 16

What is the point of omission while preforming a saccade?

Answer 16

Visual masking. responsible for lack of grey out.

Forward- masks as you change target gaze and backward- masks what you were viewing before your eyes landed on the target.

High contrast/contoured stimuli do masking best.

Question 17

Absolute saccadic refractory period vs relative saccadic refractory period?

Answer 17

Absolute: Eye moved to new target and stayed out at the new position for 200 ms. Time of latency.

Relative: IF a new stimulus is shown within a very brief period, the first shift in position is often ignored. Over ride the system.

Question 18

Frontal eye field damage results in:

Answer 18

Impaired saccadic motion of the side opposite of the lesion. Ex: damage to the left frontal lobe= impaired saccades on the right side. Eyes may drift to the left (side of injury) and pt may position head to the right to correct for this.

Usually short lived.

Question 19

Yarbus

Answer 19

Older painting. He demonstrated how our eye paths change based on instruction.

Question 20

Neural inhibition. Why is this beneficial for us?

Answer 20

Perceptual mechanism of filtering and selection. Plays a role in cognitive functions such as decision making. Just because you think about something, doesn’t mean you have to do it. Inhibition. Gives us flexibility on what we choose to gather from the environment. Gives us choice.

Question 21

Internalization and motor imagination

Answer 21

While muscles may not move, the neurons fire exactly the same as if one was actually making the movement. Ex: visualize a free throw. No motion. Neurological signals are still going to muscles. Inhibition at the very last gate.

Question 22

A saccade is a decision to act. Not a response to a stimulus.

Answer 22

:)