Chapter 18 Pursuit

Question 1

C18

What is the function of pursuit eye movements in Schor’s system? What directions do pursuit eye movements respond it?

Answer 1

Foveal gaze lock

-they hold gaze on a stationary or slowing moving objects in the environment moving laterally (up, down, sideways)

Question 2

C18

How do optokinetic and pursuit eye movements differ? In what way are they the same?

Answer 2

DIFFER
-optokinetic eye movements are used to keep the whole environment stable on the retina

-pursuit eye movements are used to follow individual objects that are moving within the environment

SAME
-both eye movements help to reduce motion blur

Question 3

C18

Describe the various candidates for stimulus to pursuit. Which of these is the primary stimulus to pursuit?

Answer 3

VISUAL STIMULI

• primary stimulus: to match eye velocity to perceived target velocity
• target acceleration
• target position

NON-VISUAL STIMULI

• auditory stimuli
• moving target by hand increases accuracy

Question 4

C18

At what speed of target motion might you begin to have difficulty pursuing a target?

Answer 4

• anything above 100 degrees per second the eye would start to have difficulty pursuing a target
• pursuit gain is very good at velocities up to 30 degrees per second

Question 5

C18

What is the role of the saccadic component of the pursuit response?

Answer 5

• before the pursuit system can lock the gaze on a moving object, saccade eye movements are used to place the gaze on the object initially
• catch-up saccades are used to correct accumulated position error behind the object that it is pursuing
• rarely, back-up saccades may be seen if the eye travels too far ahead of the object it is pursuing

Question 6

C18

With nothing more than your trusty fixation wand, how could you demonstrate the dual-mode behavior of pursuit?

Answer 6

• move the wand slowly to demonstrate primary smooth phase responses
• move the want progressively faster to demonstrate catch-up saccades

Question 7

C18

Is it possible to produce voluntarily a pursuit eye movement? How could you demonstrate this?

Answer 7

Yes and No.

Pursuits are initiated by attention to an object, so in that sense they are voluntary. But they cannot be elicited voluntarily in the absence of a moving object.

Question 8

C18

Below are listed functions or characteristics of centers in the pursuit neural pathways. Can you recall which centers perform each function?

A. Processing motion of the retinal image

B. Getting ready to send signals to the motor nuclei (III, IV, VI)

C. Responding to deficient pursuit

D. Assisting when the target moves predictably

E. Receiving signals from MST, FEF and SEF, and sending signals to cerebellum

F. Working with constant velocity objects, and sending signals to the vestibular nuclei

Answer 8

A. MT - middle temporal area, MST - midial superior temporal area

B. vestibular nuclei

C. dorsal vermis lobules VI and VII

D. FEF - frontal eye field, SEF - supplementary eye field

E. DLPN - dorsolateral pontine nuclei

F. paraflocculus (focculus)