Problem 3

Question 1

What are the functions of color vision ?

Answer 1

1. Signaling function
   ex. traffic light red = stop
2. Perceptual organization
3. Object segregation
   ex. : finding fruit in forest (crucial to survival)
4. Recognizing objects
   ex. : Banana = yellow

Question 2

Basic colors

Answer 2

• red
• yellow
• green
• blue

Question 3

Extraspectral colors

Answer 3

Do not appear in the spectrum

–> brown / purple

Question 4

Saturation

Answer 4

A colors saturation is changed by adding white
–> this decreases it

ex.: red + white = pink ( less saturated )

Question 5

How do you create a variety of colors ?

Answer 5

By changing the

a) wavelength
b) intensity
c) saturation

Question 6

Chromatic color/

Hue

Answer 6

Light reflection is a-similar across the full spectrum

–> some wavelenghts are reflected more than others

ex.: red, green , yellow, blue ( basic colors )

Question 7

Achromatic color

Answer 7

Light reflection is similar across the full spectrum

–> contains no hue

ex.: black, grey, white

Question 8

Selective transmission

Answer 8

Only some wavelengths pass through the object or substance of transparency to create chromatic color

ex.: cranberry juice selectively transmits LW light

Question 9

Additive color mixture

Answer 9

Mixing lights, which involves adding up the wavelengths if each light in the mixture

ex. : yellow light + blue light = white light
- -> reflects the sum of the wavelengths

Question 10

Subtractive color mixture

Answer 10

Mixing paints, which causes fewer wavelengths to be reflected

–> when mixed, both paints absorb the same wavelengths as when they are alone

–> wavelenghts reflected are those that are reflected by both paints in common

ex.: yellow + blue = green, because both reflect M wavelengths

Question 11

What are Wavelengths ?

Answer 11

WL are energy

–> colors are created by our perceptual system

Question 12

Trichromatic theory of color vision

Answer 12

Color vision depends on the activity of 3 different receptor mechanisms

–> describes what is happening at the beginning of the visual system

Question 13

Young - Helmholtz theory of color vision

Answer 13

Light of a particular WL stimulates the 3 receptor mechanisms to different degrees and the pattern of activity in the 3 mechanisms results in the perception of color

–> each WL is represented in the NS by its own pattern of activity in the 3 receptors

Question 14

Metamerism

Answer 14

2 physically different stimuli are perceptually identical

Question 15

Are 3 receptor mechanisms necessary for color vision ?

Answer 15

1. color vision is possible with 2 receptor types, but not one
2. a person with only one visual pigment can match any WL in the spectrum by adjusting the intensity of any of the WL

–> a second pigment is although needed to distinguish between the WLs independent of light intensity

Question 16

Color deficiency

Answer 16

Partial loss of color perception

–> associated with problems with the receptors in the retina

Question 17

Monochromat

Color Blindness

Answer 17

Type of color deficiency in which only one WL is needed to match any color in the spectrum

• -> no functioning cones
• -> sees only in shades of grey

Question 18

Dichromat

Answer 18

Needs 2 WLs to match all other WLs in the spectrum

• -> experience only some colors
• -> inherited through a gene located on X chromosome (more men are affected, because they don’t have a second X chromosome like women)

Question 19

Opponent process theory

Answer 19

Color vision is caused by opposing responses

–> happens for blue + yellow ; green + red ; black + white
(some receptor cells might be stimulated by red, but inhibited by green, while others do the opposite)

–> this theory describes events happening later in the visual system

Question 20

Behavioral evidence for the opponent process theory

Answer 20

Viewing a green (blue) field results in a red (yellow) afterimage and vice versa

Question 21

Simultaneous color contrast

Answer 21

Describes an effect that occurs when surrounding an area with a color that changes the appearance of the surrounded area

–> this explains afterimages

Question 22

Opponent neurons

Answer 22

Respond with an excitatory response to light from one part and an inhibitory response to light from another part of the spectrum

–> they are responsible for perceptual experiences like

a) afterimages
b) simultaneous contrast

Question 23

Why are opponent neurons necessary ?

Answer 23

The firing of opponent cells transmits information about wavelength more efficiently than the information contained in the receptor response

Question 24

Color constancy

Answer 24

We perceive the colors of objects as being relatively constant even under changing illumination

–> without color constancy the color of an object would depend on how it was illuminated

Question 25

Tungsten light

Answer 25

WL distribution of a light bulb

–> contains much more energy at long WLs (light appears yellow)

–> decreases your eyes to sensitivity to long WLs due to adaptation to it

Question 26

Sunlight

Answer 26

contains equal amounts of energy at all WLs (white light)

Question 27

Chromatic adaptation

Answer 27

Prolonged exposure to chromatic color

ex.: adaptation to red light will selectively bleach LW cone pigments - decreasing sensitivity to it

Question 28

Memory color

Answer 28

Knowledge about the usual colors of objects in the environment helps us achieve color constancy

Question 29

Lightness constancy

Answer 29

We see whites/ grey/ blacks/ as staying about the same shade under different illuminations

–> when it occurs it is determined by the objects reflectance

Question 30

Object reflectance

Answer 30

The proportion of the light that the object reflects into our eyes

Question 31

Ratio principle

Answer 31

When the ratio of reflectance of the object to the reflectance of surrounding objects remains the same, the perceived lightness will remain the same

–> works best for flat + evenly illuminated objects

Question 32

Reflectance edge

Answer 32

Edge where the reflectance of two surfaces changes

–> usually du to differing materials

Question 33

Illumination edge

Answer 33

Edge where the lighting changes