Week 10: Perception

Question 1

How can colours be changed?

Answer 1

• Intensity
• Saturation (adding white to colour results in less saturated colour)
• Wave length

Question 2

What is the relationship between wave length and colour perception?

Answer 2

Colour perceptions is related to the wavelength of light:

–400 to 450nm appears violet
–450 to 490nm (SHORT) appears blue
–500 to 575nm appears green (MEDIUM)
–575 to 590nm (LONG AND MEDIUM) appears yellow
–590 to 620nm appears orange
–620 to 700nm (LONG) appears red

Long , medium, AND short = white.

Question 3

How are colours of objects determined?

Answer 3

By the wavelengths that are REFLECTED

Question 4

What are “reflectance curves”?

Answer 4

Plots of percentage of light reflected for specific wavelengths

Question 5

What are chromatic colours or hues?

Answer 5

Objects that
preferentially reflect some wavelengths
AKA selective reflectance

Question 6

What are achromatic colours?

Answer 6

Containing no hues. White black, and gray tones

Question 7

What does the trichromatic theory of colour vision, proposed by Young and Helmholtz in the 1800s, state?

Answer 7

All colours in the spectrum can be produced by combining red, green, and blue. There are three receptor types in the eye each sensitive to specific colour: red, green and blue light

Question 8

What is the name for the colour receptors that we have in our eyes? And how many types of ___ do we have?

Answer 8

Cone receptors

Three

Question 9

What did the colour matching experiment show about observers with normal colour vision? What about those with colour deficiencies?

Answer 9

Normal colour vision = at least three primaries to make the matches

Deficient colour vision = less than 3 primaries

Question 10

True or false: there are pigments in the eye that respond to short/medium/and long wavelengths

Answer 10

True

Question 11

So how does colour perception occur with these different cones?

Answer 11

Depends on wavelengths available. Combinations of the responses across all three cone types lead to perception of all colours.

Question 12

What is a seeing colour like for a monochromat?

Answer 12

– A very rare hereditary condition
– Only rods and no functioning cones
– Ability to perceive only in white, gray, and
black tones
– True colour-blindness
– Poor visual acuity
– Very sensitive eyes to bright light

Question 13

What is seeing colour like for a dichromat?

Answer 13

• There are three types of dichromatism:
– Protanopia affects 1% of males and .02% of
females
>Individuals see short-wavelengths as
blue
>Neutral point occurs at 492nm (grey
instead of green)
>Above neutral point, they see yellow,
then grey instead of red
>They are missing the long-wavelength
pigment

Question 14

What is the Opponent Process Theory of Colour Vision?

Answer 14

•Proposed by Hering (1800s)
–Colour vision is caused by opposing
responses generated by blue and yellow, and
by green and red.
•Behavioural evidence:
–Types of colour blindness are red/green and
blue/yellow.
–Colour afterimages and simultaneous colour contrast show the opposing pairings

Question 15

What is the Opponent-process mechanism proposed by

Hering?

Answer 15

– Three mechanisms - red/green, blue/yellow,
and white/black
– The pairs respond in an opposing fashion to
the absorbance of light, such as positively to
red and negatively to green
– These responses were believed to be the result of chemical reactions in the retina.

Question 16

How do the opponent neurons (in opponent-process) respond?

Answer 16

They respond in an excitatory manner to one end of the spectrum and an
inhibitory manner to the other

Question 17

So what do Trichromatic and Opponent-Process

Theories Combined explain?

Answer 17

Zone Theories.

• Each theory describes physiological
mechanisms in the visual system

Question 18

What does Trichromatic theory explain?

What do opponent-process theory explain?

Answer 18

– Trichromatic theory explains the responses of
the cones in the retina
– Opponent-process theory explains neural
response for cells connected to the cones further in the brain

Question 19

How do we make sense of a 3D world when we see in 2D?

Answer 19

Depth perception: an approach that focuses on information in the retinal image. We learn the connection between cue and depth, and association becomes automatic through repeated exposure

Question 20

What are oculomotor cues?

Answer 20

Based on sensing the position of the eyes and muscle tension.

– Occular Convergence - inward movement of
the eyes when we focus on nearby objects
– Accommodation - change in the shape of the
lens when we focus on objects at different
distances

Question 21

What is occular convergence?

Answer 21

Inward movement of the eyes when we focus on nearby objects

Question 22

What are monocular cues?

Answer 22

Come from one eye.

– Pictorial cues sources of depth information
that come from 2 D images, such as pictures