Lecture 32: Visual System 3: Extrastriate cortex

Question 1

What are submodalities in vision?

Answer 1

Color, motion, depth, texture

Question 2

Where are these submodalities represented?

Answer 2

Extrastriate cortex or anywhere that’s beyond V1

Question 3

What is achromatopsia?

Answer 3

Normal color vision at the retinal vision but yet the patient can’t see any color (cortical deficit)

Question 4

What is akinotopsia?

Answer 4

Where you can’t see motion

Example: man who fears crossing traffic because people keep disappearing and reappearing in new and unexpected locations

Question 5

What is Brodman’s area 17?

Answer 5

Striate cortex

Question 6

What is Brodman area 18?

Answer 6

Second visual area (V2)

-locate surrounding V1

Question 7

How is V2 (extrastriate) organized?

Answer 7

They are retinotopically organized

• divided into Ventral and Dorsal pathways
• has modules with in it like the ChromaOxidase Blob
• blobs and inerblobs just differently oriented
• three types of bands…thick stripe, inner stripe and thin stripe

Question 8

Where is the dorsal pathway of the extrastriate? What is its function?

Answer 8

It is in the caudal parietal lobe

Function: landmark discrimination…where shit is

Question 9

Where is the ventral pathway of the extrastriate? What is its function?

Answer 9

Inferotemporal lobe
Function: Object Discrimination
Recognizes the “What”

Question 10

What are the two areas of the extrastriate we need to be familiar with?

Answer 10

1. MT in V2

2. V4 in extrastriate

Question 11

What is MT? Function?

Answer 11

Abbreviation for middle temporal lobe
-most important part of extra striate
Function: Allows you to see motion
Palmer asserts it is the “homounculus for motion”

Question 12

Why is the MT the “homunculus for motion”?

Answer 12

All MT cells are direction but not orientation selective
-represent a columnar system
-lesions of MT produce selective deficits in detecting/discriminating motion
Example: akinotopsia…you cant pour tea properly because you can’t see that shit fill up

Question 13

What is the mechanism for MT to keep track of motion?

Answer 13

Allows for smooth pursuit eye movements

• lesions of MT abolish ability to perceive structure from motion and conduct smooth pursuit eye movements
• cells in MT solve a high level problem in motion perception – the aperture problem

Question 14

What is the aperture problem? And how does MT solve it?

Answer 14

Having a lesion to the MT is like looking at a room through an aperture (a small ass hole)
Consequence: if a big object moves past the aperture, you can’t tell which direction it is traveling because hole is too small
MT solves this by having multiple apertures and combining outputs of V1 cells

Question 15

What do lesions in MT lead to?

Answer 15

Loss of ability to detect motion

Question 16

What is V4? Function?

Answer 16

Area in extrastriate in the inferotemporal lobe
Quintessential area for ventral stream (used for recognition)
-majority of cells are COLOR-coded
-orientation selective, color-coded cell for first time
-allows you to understand differences in BRIGHTNESS, even though the item maintains the same color…thereby solving the color constancy problem

Question 17

What is the Color constancy problem?

Answer 17

The phenomenon in which color can be changed by a. the source of emittance and b. the change that occurs upon reflection
However, brain makes guess about illumination of object and corrects for this change…therefore can accurately determine color

Question 18

What do lesions in V4 produce?

Answer 18

Produces achromatopsia in man

Question 19

What are the symptoms of a Posterior parietal lesion?

Answer 19

Contralateral NEGLECT (neglect of space)
-old lady who was always hungry (because she only ate from half her plate)

Question 20

What are the symptoms of an Inferotemporal lesion?

Answer 20

Agnosia: can’t tell the difference between objects
Prosopagnosia: can’t recognize faces…can’t recognize own face in mirror

Question 21

How does object and face recognition relate with one another in the cortex?

Answer 21

Objects and face recognition area are in competition with one another
-so you can be good at identifying one while not great at identifying another

Question 22

What is the pathway for the dorsal stream (the Where)?

Answer 22

M ganglion cells (M-cells) in the retina  M-cells in LGN  Layer IVC(alpha) in V1  Layer IV(beta)  thick stripes in V2  MT in extrastriate cortex  Posterior Parietal Area

Question 23

What is the pathway for the ventral stream (the what/who)?

Answer 23

P ganglion cells (P-cells) in the retina  LGN  layer IVC(beta) in V1  CO blobs in V1  thin stripes  V4  ITC

Question 24

What is the Posterior parietal area (PPA)?

Answer 24

The final point in the dorsal stream pathway

Question 25

What is the inferotemporal cortex (ITC)?

Answer 25

The final point in ventral stream pathway

Question 26

What is the ultimate role of P-cells? What pathway is it involved with?

Answer 26

To distinguish the “what” of the world
Ventral Pathway
High spatial/color resolution

Question 27

What is the ultimate role of M-cells? What pathway is it involved with?

Answer 27

To detect motion

Dorsal pathway

Question 28

What is MT in humans?

Answer 28

V5