Lecture 7: Perception of colour and form

Question 1

Perceptual segregation

Answer 1

helps to distinguish between different objects

Question 2

Signalling

Answer 2

to give meaning to what we see, helps make a decision

Question 3

Hue

Answer 3

=the property of the wavelengths of light

the colour itself eg red, blue

Question 4

Saturation

Answer 4

=the purity of the hue

(how much neutral colour is present

Question 5

Brightness

Answer 5

=perceived intensity of the hue

Question 6

What can we see between?

Answer 6

400 and 700m wave length

*can’t see ultra violet or infa red

Question 7

Context

Answer 7

• the surround can affect the perceived value

- colour constancy: different colours appear to be the same

Question 8

Rods

Answer 8

• 120 million
• scotopic vision (poor acuity)
• absent in the fovea
• sensitive to light
• night vision
• perception of movement

Question 9

Cones

Answer 9

• 6 million
• photopic vision (good acuity)
• few cones at the periphery
• not very sensitive to light
• colour vision

Question 10

Trichromatic theory

Answer 10

• 3 types of cones, especially sensitive to blue, green, and red.
• if all 3 cones stimulated by equal amount of blue, green and red, we perceive light as white

-normal colour vision is based on the activity of 3 types of receptors, each with different peak sensitivity

Question 11

Colour afterimage

Answer 11

=visual illusion in which retinal impressions persist after the removal of a stimulus

Question 12

Opponent process theory

Answer 12

six colours and three pairs of colour receptors:
red-green; blue-yellow; black-white
Members of each pair work in opposition
=> Can explain color afterimages, and why we cannot see a “reddish-green” or “yellowish-blue”

*activation of one member of the pair inhibits activity in the other

Question 13

Explanation of colour after image: opponent process theory

Answer 13

• When one member of the colour pair is “fatigued” by extended inspection, inhibition of its corresponding pair member is reduced.
• This increases relative activity level of the unfatigued pair member and results in its colour being perceived

Question 14

Which theory is correct?

Answer 14

The trichromatic theory explains colour vision phenomena at the photoreceptor level; the opponent-process theory explains colour vision phenomena that result from the way in which photoreceptors are interconnected neutrally

Question 15

Colour blindness: problem with the receptors

Answer 15

Dichromacy: Vision with only two of the three cone classes
-protanopia: no L cones

• deuteranopia: no M cones
• tritanopia: no S cones
• Monochromacy
• Rod monochromacy: no cone cells, only rod vision

*Cone monochromacy: only a single kind of cone

Question 16

Colour blindness: problems with the brain

Answer 16

Cerebral chromatopsia: lesions in the visual cortex, usually V4, colour blind

Question 17

Figure ground processing

Answer 17

• Visual system simplifies the visual scene into a figure that we look at and a ground which is everything else and forms the background
• Generally when you see one of the perceptions, the other region forms a background and is not seen, so to see both percepts requires switching back and fourth

Question 18

Grouping

Answer 18

=determining which regions and parts of the visual scene belong together as parts of higher order perceptual units such as objects or patterns.

Question 19

Grouping Laws

Answer 19

• proximity
• symmetry
• similarity
• continuity
• closure
• common fate
• likelihood