Week 6 - topic 2

Question 1

6 layers of neurons in the LGN

Answer 1

• Three layers receive input from ganglion cells of
the contralateral eye
• Three layers, receive input from ipsilateral eye

• Magnocellular layers: two inner layers
• Parvocellular layers: four outer layers
• Koniocellular sublayers: beneath other two types

Question 2

Dyslexia and visual processing

Answer 2

Some theories have suggested that dyslexia is related to magnocellular mediated visual processing

Question 3

The striate cortex

Answer 3

• the first cortical region involved in combining information from several sources. It also does some additional processing of the information transmitted from the retinas, before transmitting the information to the visual association cortex (extrastriate cortex)
• The striate cortex of one hemisphere of the brain contains a map of the contralateral half of the visual field. We call this retinotopic or topographic mapping.
• A large part of the striate cortex is devoted to analyzing information coming from the fovea, which (as you know) corresponds to a very small area of the visual field

Question 4

Extrastriate cortex - visual association cortex

Answer 4

• The striate cortex processes some basic elements of visual perception, for instance, the orientation of lines.
• However, in order to process more complex visual information, the extrastriate is necessary. It combines pieces of visual information from the striate cortex to perceive objects and entire visual scenes.
• The extrastriate cortex consists of several regions (labelled V2-V5), each which have individual maps of the visual field.

Question 5

V2-V5 processing in the extrastriate cortex

Answer 5

The type of information processed in each region is somewhat specialized.
• Neurons in one region might be specialized to process colour.
• Neurons in another region might be specialized to process movement -> You can think of the regions as being a bit like a hierarchy
• V1 receives information from “lower” regions
• Passes information to “higher” regions (e.g. V2 to
V3)

Question 6

Dorsal and ventral streams

Answer 6

• Dorsal stream (Where) Processes where object is located; speed and direction of movement
• Ventral stream (What) Processes what an object is and it’s colours