chapter 9 part 2

Question 1

opponent process theory of color vision

Answer 1

idea that there are pairs of colors that have opponent, or opposite responses

hering’s opponent process theory states that there are two pairs of chromatic colors:
- red green
- blue yellow

Question 2

two types of behavioural evidence for opponent process theory:

Answer 2

phenomenological and psychophysical

Question 3

phenomenological evidence

Answer 3

based on people’s experience when they look at colors and central to Hering’s proposal of opponent process theory

based on describing the appearance of colors

Question 4

Hue scaling

Answer 4

procedure in which ps are given colors form around the hue circle and told to indicate the proportions of red, yellow, blue, and green that they perceive in each colors

used to determine the primary colors - because each of the primaries were pure

Question 5

hering’s primary colors

Answer 5

red, yellow, green, and blue - hering proposed that each of the other colors are made up of combinations of these primary colors

Question 6

unique colors

Answer 6

name given by ewald hering to what he proposed were the primary colors: red, yellow, green, and blue because they are not made up of any other colors

Question 7

psychophysical evidence

Answer 7

quantitative measurements of the strengths of the blue-yellow and red-green components of the opponent mechanisms

hue cancellation experiments

Question 8

hue cancellation experiments

Answer 8

procedure in which a subject is shown a monochromatic reference light and asked to cancel it out with another color
- ex. how much yellow needs to be added to blue in order to cancel out all of the blueness

these experiments provided support for opponent process theory

Question 9

physiological evidence

Answer 9

discovery of opponent neurons

Question 10

opponent neurons

Answer 10

neurons that have an excitatory response to wavelengths in one part of the spectrum and an inhibitory response to wavelengths in the other part of the spectrum

provided physiological evidence for the opponency of color vision

Question 11

circular single opponent cortical neuron

Answer 11

centre surround - firing increases in centre (medium wavelength) and decreases in surround (long)

responds to large areas of color

Question 12

circular double opponent neuron

Answer 12

firing increases w medium wavelength in centre and long wavelength in surround - however, firing decreases when wavelengths are presented in opposite spaces

responds to color patterns and borders

Question 13

side by side double opponent cortical neurons

Answer 13

increases firing when a vertical medium wavelength bar is presented to the left side and when a vertical long wavelength bar is presented to the right side and decreases firing when the wavelengths are presented to the opposite sides

respond to large areas of color

Question 14

criticisms of unique hue theory

Answer 14

• the wavelengths that cause maximum excitation and inhibition don’t match the wavelengths associated with the unique hues
• hue scaling experiments also work with different primary colors

Question 15

alternative functions of opponent neurons

Answer 15

indicate the difference in responding of pairs of cones

can compare the excitatory and inhbitory responses in each cone to determine the overall response of the pair
ex. +L -M neuron has a negative response to 500nm light because the M receptor has a larger inhbitory response than L’s excitatory response

Question 16

how is color represented in the cortex

Answer 16

color processing is distributed across a number of cortical areas rather than confined to one area

interestingly, 72 percent of patients with achromatopsia (color blindness) also have prosopagnosia

Question 17

color constancy

Answer 17

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

partial color constancy occurs when our perception of hue changes a little when the illumination changes, though not as much as we might expect from the change in the wavelengths of light reaching the eye

Question 18

color constancy

Answer 18

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

partial color constancy occurs when our perception of hue changes a little when the illumination changes, though not as much as we might expect from the change in the wavelengths of light reaching the eye

Question 19

chromatic adaptation

Answer 19

prolonged exposure to chromatic color - This adaptation can cause a decrease in sensitivity to light from the area of the spectrum that was presented during adaptation

means that different types of light only have slight effects on our perception of color

responsible for color constancy

Question 20

memory color

Answer 20

the effect on perception of prior knowledge of the typical colors of objects

because people know the colors of familiar objects, they judge these familiar objects as having richer, more saturated colors than unfamiliar objects that reflect the same wavelengths

Question 21

when does color constancy work best

Answer 21

when an object is surrounded by objects of many different colors

and when objects are viewed with two eyes (better depth perception)

and when objects are viewed in a three dimensional scene

Question 22

lightness constancy

Answer 22

the constancy of our perception of an object’s lightness under different intensities of illumination

Question 23

what does the intensity of light reaching the eye from an object depend on?

Answer 23

• illumination - total amount of light that is striking the object’s surface
• reflectance - the proportion of light that the object reflects into our eyes

Question 24

what happens to illumination and reflectance when lightness constancy occurs

Answer 24

the perception of lightness is determined by the object’s reflectance instead of the intensity of illumination

related not to the amount of light reflected, but the percentage of light that is reflected

Question 25

ratio principle

Answer 25

when the illumination is the same over an entire object, lightness of the object is determined by the ratio of reflectance of the object to the reflectance of surrounding objects - as long as this ratio stays the same, the perceived lightness will stay the same

works well for flat, evenly illuminated objects but gets more complicated in three dimensional scenes

Question 26

reflectance edge

Answer 26

an edge where the reflectance of two surfaces changes

contributes to uneven illumination and poses a problem to the perceptual system since it needs to correctly perceive it in order to accuractely perceive the actual properties of a scene

Question 27

illumination edge

Answer 27

an edge where the lighting changes - like shadows

the perceptual system needs to distinguish this from reflectance edges in order to be able to accurately perceive the scene in situations of uneven lighting