Lecture 13 - Visual Processing in the Brain

Question 1

What is the name of the pathway responsible for our conscious visual perception of the world?

Answer 1

The pathway responsible for the processing of light information and conscious visual perception of the world is called the Retinogeniculate Pathway.

Question 2

What are the the three aspects of the visual world that are important for the brain to be able to pick up on?

Answer 2

1. What things/objects are.
2. Where they are.
3. Where they are going.

Question 3

Is the visual cortex contralaterally arranged and if so, what does this mean?

Question 4

A lot of the information we know about the visual cortex and how we process light and “see” the world comes from measuring single neuron activity in animals using extracellular electrodes.
True or false?

Answer 4

True.

Question 5

What kind of organisation does the primary visual cortex have?

Answer 5

The primary visual cortex has a retinotopic organisation.

Question 6

What is cortical magnification in regards to neurons devoted to processing information from the fovea?

Answer 6

There is a greater area/number of neurons that are dedicated to processing the signals received from the FOVEA.

Question 7

What area of the primary visual cortex is devoted to processing information from the fovea?

Answer 7

The tip of the occipital lobe, or back of the primary visual cortex, contains the neurons that receive and process information from the fovea or “centre of our vision”.

Question 8

How is the primary visual cortex organised?

Hint: cortical columns that represent each different position in space in our visual field.

Answer 8

Need to look into this more.

Question 9

What are orientation-tuned simple cells and how do they allow for orientation sensitivity in the primary visual cortex?

Question 10

The visual cortex is made up of modules that specialised in processing different aspects of the light information that comes in through the eyes. e.g some areas are more specialised in processing colour or orientation or motion.
Each area is processing the light information from the whole visual field, just different aspects of that light information.

True or false?

Answer 10

True.

Question 11

What is the two-streams hypothesis of visual processing?

Question 12

What area of the visual cortex is mainly responsible for processing colour processing?

Answer 12

V4

Question 13

Where in the visual pathway do we have red - green/green -red, yellow - blue/blue - yellow ganglion cells?

Answer 13

These ganglion cells are found in the Lateral Geniculate Nucleus.

Question 14

What other functions do the neurons in V4 perform?

Answer 14

Neurons in V4 are also responsive to shape and curviture.

Question 15

What is achromatopsia? And, why is it not that common?

Hint: V4 is a small area surrounded by many other modules involved in processing other aspects of vision.

Question 16

Retinal ganglion cells, LGN ganglion cells, and V1 neurons are responsive to movement, however, they do encode direction of movement. What neurons are responsive to direction of movement?

Answer 16

The neurons that selective to direction of movement are found in V5.

Question 17

Where in the brain is V5 located?

Answer 17

Medial temporal cortex/area.

Question 18

We have neurons that are selective to biological motion. Where are these neurons located?

Answer 18

Neurons that

Question 19

What is akinetposia? And, why is not that common?

Answer 19

Inability to judge movement and speed. It is not that common, as MT/V5 is a small area surrounded by a lot of other areas, therefore, it is unlikely to get damage to V5 without damage to other areas of the cortex.

Question 20

What is a common cause of the loss of sight in one side of the visual field?

Answer 20

A stroke in the artery that supplies blood to the primary visual cortex in one hemisphere can lead to the loss of conscious vision in the side of the visual field that area is responsible for, i.e the contralateral visual field.

Question 21

Where in the primary visual cortex are the neurons that are sensitive to the signals from the FOVEA?

Answer 21

The tip of the occipital lobe.

Question 21

Where in the primary visual cortex are the neurons that are sensitive to the signals from the FOVEA?

Answer 21

The tip of the occipital lobe.

Question 22

Over-representation of the information generated in the FOVEA continues from retina to LGN to V1.
True?

Answer 22

True.

Question 23

There is a cortical column for each area of space in the primary visual cortex. True?

Answer 23

True.

Question 24

The primary visual cortex has a unique structure. What is the function and structure of V1?

Answer 24

V1 has a layered structure - 6 distinct layers. Most neurons in V1 are sensitive to orientation - simple cells and other orientation sensitive cells.
Cortical columuns are columns that extend through the layers of V1 and receive information from a particular area of the visual field. The cortical columns are further divided into CYTOCHROME OXIDASE or CO blobs and interblobs, which are sensitive to colour and orientation respectively.
The role of the V1 is to receive information from the LGN and then partially process and organise it and then send it on to V2 which in turn then sends it on to the specialised area for that particular information.

Question 25

At what level of the visual cortex does orientation tuning occur?

Answer 25

In the primary visual cortex.

Question 26

The primary visual cortex is structured in both a retinotopic manner/where things are in space, but also the orientation of those things/light sources. Si the information, at the level of the V1, is organized into where the light is coming from and orientation of the light.
true?

Answer 26

True.

Question 27

In the 1960s Hubel and Wiesel discovered something about the visual system that lead to them winning the Nobel Prize. What was it?

Answer 27

They studied the visual cortex of cats and found that in V1 there are orientation-sensitive/selective cells.

Question 28

How many modules are there in the visual cortex (that we discussed)?
What is the structure and function of these modules?

Answer 28

We discussed 6 visual modules that make up the visual cortex - V1, V2, V3, V4, V5/MT, and inferotemporal cortex.
Each module has neurons that are sensitive/receive information from each area of the visual field. Moving through the modules the neural processing becomes more complex and selective.
Each module processes information for different aspects of visiom, such as colour (v4) and motion (v3).

Question 29

What is the two-streams hypothesis of visual processing and who proposed this hypothesis?

Answer 29

Proposed by Milner and Goodale in 1992, the two-streams hypothesis of visual processing is also know as the “Where” and “What” pathways. This hypothesis proposes that we process visual information about colour and object identification along the ventral modules (especially v4) of the visual cortex and process information about where things are, such as motion, through the dorsal modules (especially v5) of the visual cortex.

Question 30

What is the inferotemporal cortex?

Answer 30

It can be considered to be part of the ventral pathway or “What” pathway of visual processing and is highly sensitive to specific object recognition. The Fusiform Face Area is in the inferotemporal cortex.

Question 31

What area/module of the visual cortex is sensitive to processing of colour information?

Answer 31

V4.

Question 32

What is hemichromatopsia?

Answer 32

If there is damage to V4 on one hemisphere, then colour perception, but not form perception, would be impaired for the contrlateral visual field.
Achromatopsia is the condition where V4 is damaged or impaired on both hemispheres.

Question 33

Why is hemi- or achromatopsia quite rare?

Answer 33

V4 is quite a small area of the cortex surrounded by many other areas responsible for processing visual signals and contributing to our visual experience. It is unlikely that v4 would be damaged and none of the other areas would be damaged.

Question 34

There are neurons that are sensitive to motion in the LGN and V1. What is it about v5 that makes is especially sensitive to motion and how does it processing information about motion differently to neurons in LGN and V1?

Answer 34

The motion-sensitive neurons in the LGN and v1 are do not process or encode information about what direction something is moving, only about IF something is moving or turning on and off. V5 encodes/processes visual information about which direction the movement is occuring.

Question 35

What is another term for V5?

Answer 35

V5 is also known as the MEDIAL TEMPORAL AREA or MT area.

Question 36

What is the MST area and what does it supposedly do?

Answer 36

The MEDIAL SUPERIOR TEMPORAL AREA is thought to work with V5 or is part of V5 to encode/decode complex, familiar types of movement, such as biological movement, spiral movement, and forward movement.

Question 37

What happens if there is selective damage to V5?

Answer 37

This is called ‘motion blindness’ or akinetopsia.

Question 38

Wavelength processing in retina becomes colour perception in V4.
Orientation tuning in V1 becomes…

Answer 38

motion perception in V5 or MT and MST areas.