Psy3051 - Perception - Chpt 9 - Perceiving Colour

Front 1

What are three functions of colour vision?

Back 1

1. help us identify ad classify things
2. facilitate perceptual organisation
3. provide an evolutionary advantage ie process scenes quickly and identify food more easily

Front 2

What are the four basic and why are they considered the four basic colours?

Back 2

red, yellow, green & blue.
because people can describe all colours in the spectrum using only and all of the four basic colours

Front 3

Describe the wavelengths of the four basic colours.

Back 3

blue - short wavelength
green - middle wavelength
yellow and red - long wavelength

Front 4

What does the colour circle shoe?

Back 4

the perceptual relationship among colours

Front 5

How many colours can people discriminate between across the spectrum?

Back 5

approximately 200 colours

Front 6

Which two colours do not appear in the spectrum and what is the collective of these colours that don't appear in the spectrum?

Back 6

purple and brown
extraspectral colours

Front 7

White consists of what?

Back 7

equal amounts of all colours across the spectrum

Front 8

How can the saturation of a colour be adjusted?

Back 8

by adding white

Front 9

What can we change to effect a change in colour intensity?

Back 9

brightness

Front 10

What three things can be changed to create about a million or more discriminable colours?

Back 10

wavelength, intensity and saturation

Front 11

What is colour perception related to?

Back 11

wavelength of light

Front 12

What is the range of wavelengths associated with perceiving colour?

Back 12

400nm to 70nm

Front 13

What are the wavelength ranges for violet, blue, green, yellow, orange and red

Back 13

violet - 400 to 450 nm
blue - 450 to 490 nm
green - 500 to 575 nm
yellow - 575 to 590 nm
orange - 590 to 620 nm
red - 620 to 700 nm

Front 14

Colours of objects are determined by the wavelengths that are what?

Back 14

reflected

Front 15

What are reflectance curves?

Back 15

plots of percentage of light reflected for specific wavelengths

Front 16

Wavelengths that are reflected more than others are called what?

Back 16

chromatic colours or hues

Front 17

The property of reflecting some wavelengths more than others is called what?

Back 17

selective reflection

Front 18

What are acromatic colours?

Back 18

colours where the light reflected is similar across the full spectrum

Front 19

How is chromatic colour created in objects that are transparent?

Back 19

chromatic colour is created by selective transmission meaning that only some wavelengths pass through the object or substance

Front 20

What is additive colour mixture?

Back 20

the mixing of lights involves the adding up of wavelengths that are reflected

Front 21

What is subtractive colour mixture?

Back 21

the mixing of paints where some wavelength are absorbed and the remainder are reflected thereby producing a new colour

Front 22

Do wavelengths have colour?

Back 22

no, it's the perceptual process that produces colour

Front 23

What are the two main theories proposed to explain colour perception?

Back 23

trichromatic theory and opponent-process theory

Front 24

Who proposed the trichromatic theory?

Back 24

Young and Helmholtz in the 1800's

Front 25

What is the main assertion of the trichromatic theory?

Back 25

that three different receptor mechanisms each with different spectral sensitivities are responsible for colour vision

Front 26

In trichromatic theory explain the colour matching experiment?

Back 26

observers were required to adjust wavelengths to match a wavelength in the test field

Front 27

What were the two key findings of the colour matching experiment in trichromatic theory?

Back 27

1. Observers with normal vision require three primaries to match all colours across the spectrum
2. Observers with colour deficiencies can match the test colour using less than three wavelengths

Front 28

What physiological evidence was found to support receptor pigment differences int he trichromatic theory?

Back 28

when absorption spectra of receptor pigments was measured they found three pigments that responded maximally to short wavelengths (419nm), medium wavelengths (534 nm), and long wavelengths (564 nm)

Front 29

What did later genetic researchers find to support the pigment differences in trichromatic theory?

Back 29

different coding proteins opsin for each of the three pigments

Front 30

Explain what colour perception is based on the response of the three different types of cones means.

Back 30

1. the three cones respond differently to different wavelengths
2. the combination of responses across all three cone types lead to perception of all colours

Front 31

What is a metamer?

Back 31

where close but different wavelengths are perceptually similiar

Front 32

What are two reasons that one receptor type can't lead to colour vision?

Back 32

1. absorption of a photon causes the same effect no matter what the wavelength is
2. any two wavelengths can cause the same response by changing the intensity

Front 33

What is a monochromat?

Back 33

only see shades of grey, that is they can match any wavelength in the spectrum by adjusting the intensity of the other wavelength

Front 34

What is a dichromat?

Back 34

only needs two wavelengths to match all other wavelengths in the spectrum

Front 35

What are the three types of colour deficiency?

Back 35

1. monochromat
2. dichromat
3. anomalous trichromat

Front 36

What is an anomolous trichromat?

Back 36

needs three wavelengths to match any wavelength, just like a trichromat, however they mix the wavelengths in different proportions and are not as good at discriminating between wavelengths that are close together

Front 37

What are the features on protanopia?

Back 37

- affects 1% males and 0.02% females
- see short-wavelengths as blue
- neutral point occurs at 492 nm (grey)
- above neutral point see yellow
- they are missing long wavelength pigment

Front 38

What are the features of deuteranopia?

Back 38

- affects 1% males and 0.01% females
- see short-wavelengths as blue
- neutral point occurs at 498 nm (grey)
- above neutral point see yellow
- they are missing medium wavelength pigment

Front 39

What are the three types of dichromatics?

Back 39

1. protanopia
2. deuteranopia
3. tritanopia

Front 40

What is a unilateral dichromatic?

Back 40

trichromatic in one eye and dichromatic in the other.
helpful to researchers as they are able to explain dichromaticism

Front 41

What are the features of monochromatics?

Back 41

- very rare hereditary condition
- only rods and no functioning cones
- ability to perceive only black, white and greyscale
- true colour blindness
- poor visual acuity
- very sensitive to bright lights

Front 42

What are the features of tritanopia?

Back 42

- affects .002% males and 0.001% females
- see short-wavelengths as bluish, sometimes green
- neutral point occurs at 570 nm - above neutral point see red
- they are most probably missing short wavelength pigment

Front 43

What is the main assertion of Opponent-process theory of color vision?

Back 43

that colour vision is caused by opposing responses generated by blue and yellow and by red and green

Front 44

What is simultaneous colour contrast proposed by opponent-process theory of colour?

Back 44

an effect that occurs when surrounding an area with colour changes the appearance of the surrounded area in an afterimage

Front 45

What two pieces of evidence support the opponent-proces theory of colour?

Back 45

1. people who are colour blind to red are also colour blind to green and people colour blind to green are also colour blind to yellow
2. colour afterimages and simultaneous colour contrast show opposing pairings of colour

Front 46

What were the three mechanisms proposed in the opponent-process theory of colour?

Back 46

three opponent neurons in the retina and LGN that responded with an excitatiry response to light from one part of the spectrum and an inhibitory response to light from another part. These are -B+W +R-G -B+Y

Front 47

What were the neural responses in the opponent-process theory believed to be a result of?

Back 47

chemical reactions in the retina

Front 48

What did single cell recording find about opponent neurons?

Back 48

1. they are located in the retina and the LGN
2. they respond in an excitatory manner to one end of the spectrum and in an inhibitory manner to the other end

Front 49

How do trichromatic and opponent-process theories combine to explain colour vision?

Back 49

trichromatic theory explains the responses of cones in the retina (s/m/l) and opponent-process theory explains the neural responses for cells connected to the cones further in the brain

Front 50

What is cerebral acromatopsia and what does it's presence support?

Back 50

it is colour blindness due to damage to the cortex and it support the idea that the cortex processes information about colour

Front 51

What is colour constancy?

Back 51

we perceive the colours of objects to be relatively constant even under changing illumination

Front 52

What principle comes into the play when perceiving a green sweater under sunlight (white) and then under tungsten light (yellow)?

Back 52

colour constancy keep the sweater green even though the object would reflect different wavelengths.

Front 53

What is chromatic adaption?

Back 53

long exposure to chromatic colour to receptor adapting (bleaching) leading to decreased sensitivity to the stimulus colour.

Front 54

Explain the chromatic adaption experiment by Uchikawa.

Back 54

1. Observer shown coloured sheets of paper in three conditions: baseline with both paper and observer in white light. observer not adapted paper illuminated in red light but observer illuminated in white light, and observer adapted where paper and observer both in red light.
2. Results showed that in baseline paper was seen as green, observer not adapted perception of green paper shifted towards red, and observer adapted perception of green paper slightly shifted to red

Front 55

What are the possible causes of colour constancy?

Back 55

1. effect of surrounding - colour constancy works best when object is surrounded by many colours
2. memory - past knowledge of an object can impact colour perception ie banana and orange

Front 56

Explain Hansens' experiment demonstrating the impact of colour memory on colour constancy.

Back 56

The adjusted a spot of light and the colour of fruit against a grey background. Spot of light appeared grey but people still perceived fruit as coloured even when it was also grey.