049 Vision - Central Vision Pathways 2

Question 1

What are the 3 levels of hierarchy in Hubel and Wiesels model?

Answer 1

Simple cells -> direction and orientation selective
Complex cells -> only orientation selective
Hypercomplex cells -> flanked by inhibitory regions with same orientation selectivity. Extension into this region will inhibit cells. Respond to more complex combinations of simple features e.g. two edges at right angles.

Question 2

What are the 3 independant channels for basic cortical module?

Answer 2

Color, shape, motion

Question 3

What do layers II and III in V1 contain?

Answer 3

Parvocellular and konio cells
Blobs are for color processing
Interblobs are for high resolution processing

Question 4

What does layer IVB do in V1?

Answer 4

Magnocellular input for moetion and sterostopia.

Question 5

Which outward projections does layer IVB project to?

Answer 5

Sends outward input to V5 (motion) and layers II and III.

Question 6

Describe the structure of V2?

Answer 6

Contains thick stripes that receive from area IVB

Contains thin stripes that receive from area II and III

Question 7

Describe the two streams from V1?

Answer 7

Dorsal stream: V1 –> V2 –> MT –> MST (parietal cortex)

Ventral stream: V1 –> V2 –> V3 –> V4 –> IT (temporal cortex)

Question 8

Which pathway does magnocellular neurons go through from V1, where is it located, and what occurs when this pathway is damaged?

Answer 8

Magnocellular neurons go through the dorsal stream in the parietal cortex. When this is damage, there will be deficits in visual guided behaviour and motion vision.

Question 9

Which pathway do parvocellular neurons go through from V1, where is it located, and what occurs when this pathway is damaged?

Answer 9

Parvocellular neurons go through the ventral stream in the temporal lobe. Damage will result in inability to identify objects (agnosia).

Question 10

What does lesions in the occipital and temporal cortices result in?

Answer 10

Associative visual agnosia
Inability to identify what you are looking at
You can copy pictures but cannot recognise what you are copying.

Question 11

Which area of the brain would lesions result in optic ataxia?

Answer 11

Superior parietal cortex because of the ventral stream.

Question 12

What is construction apraxia?

Answer 12

Mixing of both optic ataxia and associative visual agnosia. They cannot construct. and the concept is also not understood.

Question 13

What would occur with inferior parietal cortex lesions?

Answer 13

Hemispatial neglect, particularly in left field because it is usually loss in right side that causes this. Angular gyrus is critical region that can be destroyed by this

Question 14

Where would lesions take place to result in prosopagnosia?

Answer 14

Fusiform face area in lingual and fusiform gyrus in temporal lobe.

Question 15

What deficit in neurons do dyslexic subjects show?

Answer 15

Magnocellular neurons