Eye movement (Practical)

Question 1

What is the function of this piece of apparatus in the eye movement experiment?

Answer 1

Infrared oculometer: IR transducer for measuring eye position

Question 2

How does the transducer used to measure eye movements work?

Answer 2

1. An infrared emitter emits high frequency infrared pulses towards the eyes.
2. An infrared detector detects the pulses reflected from the eyes.
3. Comparator circuit in the transducer compares the amplitude of reflected light with that emitted.
4. Difference in amplitude determined by position of eyes.
5. The white sclera reflects more light compared to the darker iris. The smaller the amplitude difference, the more sclera can be detected.
6. As the eyes move, gradually more iris covers the ‘spotlight’ for IR emitter and so amplitude difference increases.

Question 3

What is the function of this piece of apparatus in the eye movement experiment?

Answer 3

• Bite-bar
• Fixes the head in place so that gaze is controlled by movements of the eyes alone.

Question 4

What distance do stimuli need to be placed at in order for 1 cm to correspond to 1^o?

Answer 4

~57cm

Question 5

What type of movements are saccades?

Answer 5

Ballistic movements

Question 6

What accounts for the extreme variability of saccades when moving the eyes by the same amount?

Answer 6

Decision time

Question 7

What is the highest frequency of scanning stimulus that can be tracked by smooth pursuit?

Answer 7

~3 Hz

Question 8

What type of eye movement is the optic fibre used to test for?

Answer 8

Convergence

Question 9

What is the difference between saccadic movements and vergence movements?

Answer 9

• In saccadic movements, the eyes move at maximum velocity for fixed period of time due to being ballistic.
• In vergence movements, the velocity is exponential. As target is reached, velocity decreases. This is because direct negative feedback is used. Because error signal decreases as target is approached, so does the velocity.

Question 10

How can optokinetic reflex be triggered?

Answer 10

Placing moving background with alternating black and white stripes in front of subject.

Question 11

How can optokinetic reflex be stopped in presence of moving background?

Answer 11

Placing stationary fixation point in front of the subject

Question 12

How can vestibular nystagmus be induced?

Answer 12

Constant rotation of the head

Question 13

What is the difference between optokinetic nystagmus and vestibular nystagmus?

Answer 13

Optokinietic nystagmus continues as long as background is moving while vestibular nytagmus stops as semicircular canals adapt.

Question 14

What are the types of gaze-holding movements?

Answer 14

1. Vestibulo-ocular reflex (VOR)
2. Optokinetic reflex (OKR)

Question 15

What are the tyoes of gaze-shifting movements?

Answer 15

1. Saccades
2. Smooth pursuit
3. Vergence

Question 16

What type of eye movement does this represent?

Answer 16

Optokinetic nystagmus

Question 17

What type of eye movement does this represent?

Answer 17

Saccades

Question 18

What type of eye movement does this represent?

Answer 18

Smooth pursuit (low/high frequency)

Question 19

What type of eye movement does this represent?

Answer 19

Vergence

Question 20

What type of eye movement does this represent?

Answer 20

Vestibular nystagmus

Question 21

What type of eye movement does this represent?

Answer 21

Saccades (while reading)