Week 7

Question 1

Why do we move eyes?

Answer 1

1. Allow the interesting parts of the image to fall onto the high resolution part of the retina
2. Converge eyes at different distances
3. Stabilise visual image on retina despite motion of the eye or the scene

Question 2

What is a gaze path?

Answer 2

The spatial path of the eye as it moves across an image

Question 3

How does gaze stabilisation work?

Answer 3

Eye movements jump from one location to another to allow a stable image to fall on the retina

Question 4

What does Yarbus (1967) show us about gaze stabilisation?

Answer 4

Eye movements are automatic and volitional

Question 5

What eye muscles control pupil diameter?

Answer 5

Intra-ocular muscles

Question 6

What is the function of extra-ocular muscles?

Answer 6

To move the eyeball within the socket, which are innervated by specific cranial nerves

Question 7

Describe the gaze stabilising mechanism

Answer 7

It is an old system to make image sharper; include OKR and VOR

Question 8

Describe the gaze shifting mechanisms

Answer 8

It is a new system to scan/track objects; include vergence movements, smooth pursuit and saccade movements

Question 9

Describe gaze fixation

Answer 9

Eyes must be held stationary between movements

Question 10

Describe OptoKinetic Reflex

Answer 10

A powerful reflex to maintain gaze position driven by motion across the whole retina (assumes the world is stationary); it is stimulated by the retinal slip

Question 11

How does the OptoKinetic Reflex allow us to track moving objects?

Answer 11

By minimising the “retinal slip” one the retina

Question 12

What does the Optokinetic Nystagmus do?

Answer 12

It alters slow drift of eye movements with rapid movements, too allow the image to stabilise

Question 13

How fast is the Optokinetic Nystagmus? And why?

Answer 13

Relatively slow because it relies on integrating vision and motion with brainstem compensatory mechanism

Question 14

What is the Vestibular Ocular Reflex?

Answer 14

A powerful reflex to maintain gaze position despite head movement

Question 15

How fast is the Vestibular Ocular Reflex? Any why?

Answer 15

Around 14ms (fast) because only 3 neurons in the brainstem are involved

Question 16

What is the process of the Vestibular Ocular Reflex?

Answer 16

1. Head movement detected by semi-circular canals
2. Balance system passes head movement signals to vestibular nuclei
3. Movement signals cross the midline and inervate OMNs which drive extra ocular muscles
4. Movement to right abducts left lateral rectus muscles and adducts the right medial rectus muscle

Question 17

What is vergence?

Answer 17

Simultaneous movements of both eyes in opposite directions to maintain focus, accommodates different viewing distances

Question 18

What is smooth pursuit?

Answer 18

Slow simultaneous movements of both eyes in the same direction > allows tracking of slow moving objects against a stationary background

Question 19

What does smooth pursuit need to work?

Answer 19

Suppression of the Optokinetic Reflex

Question 20

How fast is smooth pursuit?

Answer 20

A slow visual “feedback” mechanism because its driven by visual motion signals from MT and MST

Question 21

Describe saccades

Answer 21

Simultaneous movements of both eyes in the same direction; allows for very rapid gaze shifts, and at constant velocity

Question 22

Why do saccades need to be fast?

Answer 22

Because vision is degraded during movement, therefore, saccades minimise the amount of time the eyes are in motion

Question 23

How do you make saccades?

Answer 23

They are produced using parts of gaze stabilisation circuitry, with an extra part that tells the eyes where to look; they are controlled by burst neurons in the PPRF

Question 24

Describe Superior Colliculus

Answer 24

Performs a sensory motor transformation that orients the head and eyes towards something seen or heard

Question 25

What are the 2 different systems involved in spatial cognition?

Answer 25

1. Posteror Parietal Cortex (self to object) 2. Hippocampus (object to object navigation)

Question 26

What does the London taxi driver study demonstrate to us?

Answer 26

Greater spatial cognition and navigation leads to increased posterior hippocampal volume Storage and use of mental maps

Question 27

Describe the neurogenesis in the human hippocampus

Answer 27

About 1/3 of adult cells are renewed, with a gradual loss of cells that are in a non-renewing majority

Question 28

What role do place cells have in the consolidation of memories?

Answer 28

They provide an internal representation of space or 'cognitive map'; they also remap when the behavioural context changes

Question 29

Describe grid cells

Answer 29

They fire grid like pattern for many locations, and they combine to activate place cells for unique locations

Question 30

Where do grid cells receive information from?

Answer 30

Neocortex

Question 31

Describe the Posterior Parietal Cortex

Answer 31

Encodes object position relative to the body

Question 32

Describe Apraxia

Answer 32

Typically results from damage to left parietal lobe, causes difficulty in coordinating sequences of movements in the absence of paralysis / difficulty coordinating sequences of sounds

Question 33

Describe neglect

Answer 33

Typically results from damage to right parietal lobe, causes difficulty in detecting information about objects in external space

Question 34

What does the right and left PPC code for?

Answer 34

Right PPC: both left and right visual space Left PPC: only for right visual space

Question 35

What does the ventral process?

Answer 35

Multimodal encoding of space and motion around the head

Question 36

What does the anterior process?

Answer 36

Encodes touch, grasping and tool use

Question 37

What does the medial process?

Answer 37

Encodes reaching and pointing

Question 38

What does the lateral process?

Answer 38

Encodes intended eye movements

Question 39

Do we have prospective coding in humans? What is it?

Answer 39

Evidence would suggest yes A small proportion of place cells are turned to prospective goal location irrespective of starting position, movement speed, etc

Question 40

Where does prospection occur?

Answer 40

Involves interaction between hippocampus and prefrontal cortex