09-10. extrastriate processing

Question 1

2 main extrastriate pathways?

Answer 1

1. dorsal (dorsal fin –> dory –> top)
2. ventral

Question 2

What does the dorsal pathway connect?
(LGN layer, pathway, cortex)

Answer 2

1. MAGNO cellular layer
2. MT (middle-temporal visual area)
3. Parietal cortex

Question 3

What is the dorsal pathway most important for?

Answer 3

“where” / “how” pathway
(dOrsal = hOw)

Question 4

What is MT important for?

Answer 4

Motion perception!

Specifically direction, more than just flickering

MT = MoTion

Question 5

What does the ventral pathway connect?
(LGN layer, pathway, cortex)

Answer 5

1. PARVO cellular layer
2. V4
3. Inferotemporal cortex

Question 6

What is the ventral pathway most important for?

Answer 6

“what” pathway

venTral = whaT

Question 7

What is V4 important for?

Answer 7

• form
• color

V4 –> “FOURm” & color

Question 8

How is V4 sensitive to form and curved edges?

Answer 8

• V1 cells have preferred orientations that indicate short, straight edges
  –> V1 tells us BARS
• V4 cells combine info from V1 cells to add bars and make a CURVED edge
• curved edges important for perceiving CONTOUR / form

Question 9

How does the IT cortex perceive form?

Answer 9

• V1 = straight
• V4 = curves, contours
• IT cortex = SHAPES
• cells in IT cortex respond to combinations of contours, with relatively large receptive fields

Question 10

What experiment is the PARIETAL cortex crucial for?

Answer 10

• landmark / “where” task
• monkey learns that food is in the bin with the object near it
• with damage to PARIETAL cortex…
  –> they have trouble identifying WHERE food is
  –> struggle with SPATIAL LOCATION

Question 11

What experiment is the IT cortex crucial for?

Answer 11

• object / “what” task
• has to differentiate between a square/triangle or between red/green to get food
• with damage to IT cortex…
  –> struggle with FORM and COLOR

Question 12

What happened with the patient with ventral stream damage? What could/couldn’t she do? What does this tell us?

Answer 12

• couldn’t identify objects, but could draw pictures from memory
• couldn’t report orientation of slot, but could insert a card into it
• affected VERBAL report, NOT her ACTION
• ventral / IT is essential for identifying objects
• there might be information that a person doesn’t have conscious access to
  –> may be in the dorsal / MT pathway
  –> she was able to complete motion/action, but not perception

Question 13

Dissociating perception and action meaning…?

Answer 13

Idea that perception and action happen in different visual pathways

Ventral –> Perception (end of alph.)
Dorsal –> Action (beg. of alph)

Question 14

How to study dissociation in non neurologically compromised people?

Answer 14

Compare the effects of an illusion on…
1. judgement on appearance of stimulus (perception)
2. motor actions towards it
–> like picking it up

ex.
- small stick that looks bigger (like railroad track illusion lines)
- dots surrounded by other dots

• motor action is the same for the same physical stimulus, regardless of perception

Question 15

What is modularity?

Answer 15

Very specialized processing locations for different visual / brain functions

Question 16

Fusiform Face Area?

Answer 16

• special area to identify and perceive faces
• doesn’t work when faces are scrambled
• brain activity in FFA ONLY when participants CONSCIOUSLY perceived a face

Question 17

Extrastriate Body Area

Answer 17

• area to identify and perceive body parts

Question 18

Parahippocampal Place Area

Answer 18

• responds selectively to large-scale spatial layouts such as landscapes and buildings

Question 19

Distributed coding meaning?

Answer 19

• Objects represented by activity in many regions of the brain
• despite modularity, there’s a lot of areas involved in perceiving all sorts of things
• distributed coding is really important for effectively communicating stimuli
  –> single neurons are ambiguous