Lecture 3

Question 1

What is colour blindness?

Answer 1

The inability to see certain colours properly due to mis-tuned or missing cone types in the eyes.

Most people classified as colour blind can still see colours but have difficulty discriminating between them.

Question 2

What is cerebral achromatopsia?

Answer 2

A form of cortical colour blindness where individuals cannot consciously perceive or differentiate colours due to damage in area V8 of the brain.

They can detect brightness but not colour.

Question 3

What are centre-surround colour opponent mechanisms?

Answer 3

Mechanisms in the retina and LGN that compare colours in pairs, such as red-green and yellow-blue, to allow for colour discrimination.

This is achieved through the organization of retinal ganglion cells.

Question 4

What is colour constancy?

Answer 4

The ability to perceive the colour of an object consistently under varying lighting conditions by discounting the light source.

This process primarily occurs in area V4 and V8 of the visual cortex.

Question 5

What factors contribute to why people see the dress in different colours?

Answer 5

• Over-exposure of the image
• Different viewing angles
• Different naming of colours
• Colour blindness
• Individual differences in colour processing
• Individual experiences
• Failure of colour constancy

Question 6

What is the visible spectrum?

Answer 6

The part of the electromagnetic spectrum that human eyes can detect, which does not include ultraviolet light.

Most mammals have only two cone types, while humans and some primates have three.

Question 7

What are the types of cone photoreceptors in humans?

Answer 7

• S-cones (blue)
• M-cones (green)
• L-cones (red)
• Rods (for night vision)

Question 8

What is the most common form of colour blindness?

Answer 8

A mis-tuned green cone, leading to difficulty in distinguishing between red and green hues.

Red-green colour blindness is more common in men due to the X chromosome inheritance.

Question 9

What is the role of area V8 in colour perception?

Answer 9

Area V8 is responsible for the conscious perception of colour and is critical for colour constancy.

Damage to this area can lead to cerebral achromatopsia.

Question 10

What is the difference between simple and complex cells in area V1?

Answer 10

• Simple cells: orientation selective with distinct on/off regions
• Complex cells: orientation selective without distinct on/off regions

Question 11

What is the tilt after-effect?

Answer 11

A perceptual phenomenon where prolonged exposure to a tilted line results in the perception of an opposite tilt when viewing a straight line.

This is an example of inhibition over time.

Question 12

Fill in the blank: The colour system is arranged much like spatial vision with centre-surround cells in the retina where centre-surround prefer different _______.

Answer 12

colours

Question 13

What is simultaneous colour contrast?

Answer 13

A phenomenon where the perception of a colour is influenced by the surrounding colours, altering how that colour is viewed.

This can affect how colours in an image, like the dress, are perceived.

Question 14

True or False: The dress illusion can be fully explained by colour blindness.

Answer 14

False

Question 15

What are the two colour systems in human vision?

Answer 15

• Ancient luminance plus yellow/blue system
• Newer red/green system

Question 16

What does the term ‘water colour illusion’ refer to?

Answer 16

The phenomenon where the brain fills in the body colour of an object based on colour edges transmitted from the retina.

This filling in occurs in the cortex after the edges are detected.

Question 17

What is the significance of rods in vision?

Answer 17

Rods are photoreceptors responsible for vision in low light conditions but do not contribute to colour vision.

Humans are colour blind at night due to the lack of cone activity.

Question 18

What is the classic view of complex cells in relation to simple cells?

Answer 18

Complex cells are connected to many simple cells by an OR function.

Question 19

What type of visual information do complex cells represent?

Answer 19

A more abstract type of visual information, partially independent of location within the visual field.

Question 20

List the characteristics of complex cells.

Answer 20

• Orientation selective
• Some size selective
• No separate on/off regions
• Not position selective
• Length summation

Question 21

What distinguishes hyper-complex cells from complex cells?

Answer 21

Hyper-complex cells are sensitive to line length and orientation.

Question 22

What happens to hyper-complex cells when a stimulus is outside its ‘classical’ receptive field?

Answer 22

The cell is turned off.

Question 23

What is the significance of texture in visual perception?

Answer 23

Lack of texture can cause problems differentiating road from pavement.

Question 24

What are the statistics related to road fatalities?

Answer 24

1,700 fatalities and 184,000 injuries.

Question 25

Define texture in terms of spatial detail.

Answer 25

Spatial detail at a scale finer than the observer currently defines as the object scale.

Question 26

How does texture segmentation help in visual perception?

Answer 26

It enables us to see edges of objects defined by changes in their surface markings or makeup.

Question 27

What did Nothdurft (1990/91) find about texture segmentation?

Answer 27

Texture segmentation based on line crossings and endings is more affected by certain visual manipulations than segmentation by orientation.

Question 28

What is the simultaneous tilt illusion related to?

Answer 28

Centre-surround cells for orientation in V1.

Question 29

What is the Titchener circles/Ebbinghaus illusion?

Answer 29

An illusion where the perceived size of a central circle changes based on the size of surrounding circles.

Question 30

What occurs during inhibition over time related to colors?

Answer 30

Cells turn off where the after-effect is the opposite or complementary color.

Question 31

What happens to the perception of orientation after prolonged viewing?

Answer 31

The new orientation is not seen properly, often shifted to the opposite direction.

Question 32

What is the neural code for perceived orientation?

Answer 32

Determined by a population of cells sensitive to different orientations.

Question 33

What is the effect of adaptation on orientation-sensitive cells?

Answer 33

The response of active cells is turned down by a process called adaptation or inhibition over time.

Question 34

Summarize the key concepts related to cells in area V1.

Answer 34

* Simple cells are sensitive to orientation and position * Complex cells are sensitive to orientation only * Hyper-complex cells are sensitive to orientation and length * Hyper-complex cells may lead to the perception of illusory contours

Question 35

What are the implications of inhibition over time among orientation cells?

Answer 35

Leads to the tilt after-effect and the size after effect.