24 - Representations of the Parietal Lobe

Question 1

What is an allocentric map?

Answer 1

A map, representing where things are relative to an external reference, e.g. the North pole

Question 2

What is an egocentric map?

Answer 2

A map which represents things relative to ourselves

Question 3

What are different coordinate frames in the brain used for?

Answer 3

Different purposes and body parts and different actions

Always relative to something

Question 4

When representing the space around us, what areas of the brain have important coordinate frames for the most common body parts?

Answer 4

Eye-centered; V1, V2, V4 (different angles in visual field fire in a particular place)

Body-Centered; somatosensory cortices (similar to eye-centred, particular body part fires particular part of brain)

Head/ear-centered
Hand centered
- We don’t know any maps that are laid out for these
- Seem to be on the fly

Question 5

What is gaze angle (eye position) needed for?

Answer 5

Calculating direction for pointing, walking

Resolving whether, when retinal motion detected, did eyes or object move

Question 6

What are the possibilities for understanding where to move our eyes?

Answer 6

• Direct sensing of eye position (via proprioceptive sensation)
• Remembering where you told your eyes to move (aka efference copy)

Question 7

What are some experiments which demonstrate that humans have an efference copy rather than sense their eye position when moving their eyes?

Answer 7

Finger-in-the-eye Demo

• get sense whole room moved
• not sensing eye position
• brain is used to creating efference copy in the normal way, not when eye is poked
• but when you do this you’re deflecting other muscles not just the eye

Brindley & Merton (1960)

• lateral or medial rectus muscle seized through conjunctive with forceps and moved
• patients perceived objects moving in opposite way
• both eyes held with forceps and attempt to move eyes
• patients perceive objects moving again

When attempting to move eyes, brain is creating efference copies and perceive movement

Question 8

What do eye movement commands get sent to maps in the parietal cortex to do?`

Answer 8

Update the maps of where things are

Compensate for retinal motion, so you don’t perceive world to move when your eyes don’t move