lecture 3 - visual pathways 2

Question 1

what is the dorsal pathway

Answer 1

• considered as the “where pathway”
• involved with processing the objects spatial location relative to the viewer
• vision for action
• basically so we know where things are and can convert into motor actions

Question 2

the ventral pathway projects through where into where

Answer 2

The ventral pathway projects through V4 into areas of the inferior temporal cortex

Question 3

what is the ventral pathway

Answer 3

• known as the “what pathway”
• involved with object and visual identification and recognition
• vision for perception
• can reach out for things but might not recognise exactly what it is

Question 4

why is it important that there is a connection between the ventral and dorsal pathways

Answer 4

because it can lead to object identification and location

Question 5

Damage to the ventral pathway can cause what? explain what this is and how it may develop.

Answer 5

prosopagnosia - face blindness, inability to recognise peoples faces
- due to stroke or develop from birth

Question 6

Damage to the dorsal pathway can cause what? Explain what this is.

Answer 6

optical ataxia - the inability to accurately reach or point towards objects under visual guidance

(no issue with recognising or naming objects just locating them)

Question 7

Parallel streams from V1

Answer 7

Parallel streams from V1 originate in layers 2/3 and from layer 4B:
* Layer 4B contains direction selective cells. Parallel streams from V1
* Layers 2/3 contains colour tuned cells within the CO blobs.
* Layers 2/3 contains orientation tuned cells outside the blobs

Question 8

What is cytochrome oxidase in V2 used for

Answer 8

used for staining to visualise and study brain regions

Question 9

what are the three types of cytochrome oxidase stripes in V2

Answer 9

• thick stripes
• thin stripes
• pale stripes (interstripes)

Question 10

What are thick stripes associated with

Answer 10

direction of motion of an object and depth of an object to some extent

Question 11

What do thin stripes respond to

Answer 11

they respond to colour but also cells that care about amount of light

Question 12

Interstripes respond to what?

Answer 12

Interstripes respond to contrast but predominantly orientation based response

Question 13

Explain the V2 streams. the inputs and outputs

Answer 13

4b - thick stripes - V3 OR MT/V5 (motion processing)

Blobs - Thin stripes - V4 (colour processing)

Interblobs - interstripes - V4 (colour processing)

Question 14

General info about V2

Answer 14

• forms vision
• cells are responsible for orientation and colour
• V2 cells are also responsible to ‘illusory contours’

Question 15

V3

Answer 15

• not studied in that much depth as V1, V2,V4 or MT/V5
• magnocellularly dominated
• receives inputs from layer 4B in V1and from thick stripes in V2
• Contains a large number of cells for orientation, direction and disparity and V3 makes extensive connections back to V1 and V2 and on to V4 and MT.

Question 16

V4

Answer 16

• the third cortical area in the ventral stream
• Receives strong input from V2 (thin stripes) as well as direct connections from central V1
• Sends strong outputs to posterior Inferotemporal cortex (PIT)
• V4 is tuned for orientation and colour

Question 17

Inferotemporal cortex (IT)

Answer 17

• Information is next fed to the inferior temporal cortex
  – very large receptive fields
  – All include fovea
  – may include both hemifields i.e input from opposite cortex
  – may be further subdivided (PIT, CIT, AIT each with d and v subdivisions)
• Cells in inferior temporal cortex can be exclusively responsive to complex stimuli, such as hands, or faces
• IT cells do not generally care about the position or size of the object within the receptive field

Question 18

How information flows in ventral pathway

Answer 18

V1- V2 -V3
|
V4
|
IT

Question 19

How information flows in the dorsal pathway

Answer 19

V1 - MT - MST
V1- V2 -MT - MST
V1- V2 - V3 - MT - MST
V1 - V3 - MT - MST

Question 20

what is MT responsible for

Answer 20

• motion processing
• receives mainly magnocellular based inputs from V1 directly and indirectly from V2, V3 and V4.
• receptive fields are “direction” selective (though they do respond to orientation!) plaid patterns & moving dot clouds

Question 21

MT responds to…

Answer 21

• plaid patterns
• dots
• 3D objects

Question 22

what happens after MT

Answer 22

• Visual Information is sent to the Medial Superior Temporal Cortex (MST)
• Feeds into the next stages of the (“Where”) stream much larger receptive fields than V5(MT) (ie sums input from V5(MT)) processes “optic flow”

Question 23

what happens after the MST

Answer 23

• MST projects into the inferior parietal lobule and in particular area 7a and LIP:
• 7a and LIP are adjacent and contiguous, and reciprocally connected.
• Believed to be involved in translating from visual space to motor space to help guide movements – especially eye movements