colour perception Flashcards

Question

cones

Answer 1

photoreceptors specialized for daytime vision, fine acuity and colour respond best in high luminance conditions - high levels of light are used to process colour less sensitive to light

Answer 2

During scotopic vision, only the rods are active. This shifts your visual sensitivity into the blue range ▪ At night, red objects appear darker (black), and blue objects appear brighter (white)

Answer 3

First person to demonstrate that light behaves as a wave “Now, as it is almost impossible to conceive each sensitive point of the retina to contain an infinite number of particles, each capable of vibrating in perfect unison with every possible undulation, it becomes necessary to suppose the number limited, for instance, to the three principal colours, red, yellow, and blue.”

Answer 4

* White light occurs when all wavelengths are present in an equal amount * Monochromatic light occurs when a ray is composed dominantly of a single wavelength (e.g. “red” light) * Maxwell demonstrated that white light can be created by mixing just three types of monochromatic light * This suggests that there are only three colour channels in human vision Maxwell produced the first colour photograph (hint: it’s a ribbon) Steps: 1. Take a B&W photo with a red filter 2. Repeat with blue and green filters 3. Separately project each photo on the same area with the corresponding coloured light

Answer 5

Helmholtz’ book Treatise on Physiological Optics was a landmark publication in the science of visual perception * In it he refined the Trichromatic Theory in several ways: 1. Receptors had gaussian response curves 2. Colour sensation is encoded in the photoreceptors 3. Each receptor produced a sensation of a “unique hue.”All other colours were mixtures Demonstrated how this accounted for various types of colour blindness

Answer 6

the sensitivity of a cell or a device to different wavelengths on the electromagnetic spectrum

Answer 7

S cones, M cones, L cones

Answer 8

maximally responsive to short wavelengths 420 nm max Blue

Answer 9

maximally responsive to middle wavelengths 535 nm max Green

Answer 10

maximally responsive to long wavelengths 565 nm max Red

Answer 11

person see something, but fails to know what it is

Answer 12

inability to name, despite the ability to see and recognize them ie/ colours

Answer 13

where one stimulus evokes the experience of another stimulus ie/ sounds associate with different colour

Answer 14

inability to perceive colours that that is caused by damage to the CNS

Answer 15

all three cones but their behaviour is atypical ie/ wavelength shifts two of them so similar that these people experience world similarly to those with two cones

Answer 16

missing one cone type

Answer 17

protanopia deuteranopia tritanopia

Answer 18

protanopia and deuteranopia

Answer 19

absence of L cones

Answer 20

absence of M cones

Answer 21

absence of S cones

Answer 22

has only one cone cone see the world in shades of grey still have daytime vision no colour perception, can't compare cones

Answer 23

has only rods lack daytime vision and would hurt (poor acuity in daytime) missing cones all the time

Answer 24

inability to perceive colours, despite functioning photoreceptors and early visual stages; typically due to brain damage trichromic theory cannot explain

Answer 25

Words like blue, not sky blue Used with high frequency , and have meanings Agreed upon by speakers of a language Common Higher m cones “green” Lower m cones “reddish orange” For a deutemope with no m cones their remainer L and S cones will produce same response single words that describe colours and have meanings that are agreed upon by speakers of a language 11 terms have broad agreement (American)

Answer 26

Rare situation where the colour of any light is defined by the relations of 4 numbers—the outputs of those receptor types

Answer 27

“[Helmholtz] paid no attention whatever to the fact that, while the necessary stimuli for all the colours in the spectrum (and in the world) can be secured by appropriate mixtures of only three wave-lengths, the distinct, different, sensations that result are not three in number but five – yellow and white are just as good, just as unitary, light-sensations as are red, green, and blue.”

Answer 28

We are not typically exposed to single wavelengths How do we discriminate from injured apples, or ones exposed to sun Rest of nervous system only knows what the cones tell it Mixtures of wavelengths that look identical If two different set of wavelengths stimulate the cones in the same way, even thought the lights are physically different, the bran interprets it as same colour Green and red identical wavelengths appear yellow Tells us that colour perception is also determined by how wavelengths interact

Answer 29

a visual image seen after a stimulus has been removed

Answer 30

an afterimage whose polarity is the same as would the original stimulus now & We tell the Very brief (<500 ms)

Answer 31

an afterimage whose polarity is the opposite of the original stimulus Colour specific adaption Light stimuli> dark afterimages Light stimuli produce dark negative afterimages Colors are complementary(opponent) Red>Green, Green>Red Blue>Yellow, Yellow>Blue

Answer 32

A stimulus who’s removal produces a change in visual perception or sensitivity

Answer 33

Point at which an opponent colour mechanism is generating no signal Ie/ wavelength or combination of wavelengths cancel each other out—visual system will just perceive grey

Answer 34

Ewald Hering (1843 – 1918) proposed an alternative theory of colour vision based on opponent colours “Orange” is perceived as a reddish-yellow “Purple” is perceived as a blueish-red BUT there is no such thing as a reddish-green or yellowish-blue Hering suggested that colour sensations are produced by the output of three antagonistic processes Red-green Blue-yellow Black-white

Answer 35

The Trichromatic theory was correct as a theory of receptors. Three types of photoreceptors do exist. Opponent process theory predicts that colour is not encoded at the receptors, but later in the system The input from the cones is carried to the cortex along two opponent channels

Answer 36

Opponent process required for hue encoding: Colour opponency without spatial opponency Opponent process found in retina Colour and spatial opponency

Answer 37

both: helmhltz was right that the initial stage involves three types of photoreceptors hering was correct that there was an essentially antagonistic, opponent process in the initial stages of colour vision Neither: neither of these processes is sufficient for "hue perception" the "unique hues" still elude scientists we still don't understand the entire process of colour vision

Answer 38

Neither the opponent process theory, nor the trichromatic theory account for how colour vision evolved. All animals can discriminate white from black. (oldest system) Bees (and other animals) have strong yellow-blue discrimination, but weak red- green discrimination. (newer system) Humans have good, red-green discrimination. But it gets weaker in the periphery. (newest system)

Answer 39

Contemporary evolutionary theory aligns with the original Ladd-Franklin theory in many respects. Ladd-Franklin got the physiological mechanism of cone differentiation incorrect But she did identify the appropriate evolutionary sequence ~stages in evolution of colour vision panel c shows the spectral sensitivity curves of the three photosensitive pigments in the normal human eye. Ancestral mammals are thought to have had dichromatic vision.At an intermediate stage the spectral separation of the long wave/middle wave pigments may have been small, and dependent on a single amino-acid difference between the two proteins~

Answer 40

General agreement on colours Basic colour terms: single words that describe colours and have meanings that are agreed upon by speakers of a language 11 terms have broad agreement (American) But, various cultures describe colour differently Colour boundaries are pretty sharp More likely to be confused if the colour has a different label cultural relativism sapir whorf hypothesis

Answer 41

in sensation and perception, the idea that basic perceptual experiences (e.g., colour perception) may be determined in part by the cultural environment

Answer 42

Your perception is limited by your range of concepts. If you don’t have a concept for something, you cannot see it. If you didn’t have a term for blue, you wouldn’t be able to see it

Answer 43

private conscious experiences of sensations or perception Only your experience

Answer 44

When many colours are present, as is typical in natural scenes, they can influence each other Colour contrast: a colour perception effect in which the colors in surrounding colour of one region induces the opponent colour in a In the environment neighbouring region colors in in surrounding In the environment push colour in a certain direction

Answer 45

a colour that can be experienced in Isolation.

Answer 46

a colour seen only in relation to other colors Ie/gray, brown

Answer 47

When many colours are present, as is typical in natural scenes, they can influence each other a colour perception effect in which two colours bleed into each other, each taking on some of the chromatic quality of the other Scenes can contain colours that can’t be experienced in isolation Apparent colour comes from the stripes passing the the object

Answer 48

Lightness (whiteness) constancy: the tendency of a surface to appear the same lightness despite variations in the intensity of illumination Achieved by discounting the illuminant and determining the true lightness of a surface regardless of how it appears Achromatic (Black > White) Lightness/whiteness – the apparent reflectance (albedo) of a surface Black reflects little Grey reflects an intermediate amount White reflects a lot Not dependent on the actual amount of light reaching your eye Edges; Reflectance edge: edge where reflectance properties of two surfaces change Illumination edge: edge where illumination changes Visual system has to determine if a change in the amount of light reaching the retina is due to a reflectance edge (lightness change) or illumination edge (shadow) Identifying Illumination Edges; Meaningful shape, Penumbra, Change in surface direction Explanation; Adaption, Photoreceptors will adjust to average light level—within an environment Anchoring Principle- The brightest part of a scene will be seen as “white,” the darkest will be seen as “black” Ratio principle- Comparison of reflectance ratios of nearby surfaces

Answer 49

edge where reflectance properties of two surfaces change

Answer 50

edge where illumination changes

Answer 51

the light that illuminates a surface - it is not constant

Answer 52

photoreceptors will adjust to average light level within an environment

Answer 53

the brightest part of a scene will be seen as "white," the darkest will be seen as "black"

Answer 54

comparison of reflectance ratios of nearby surfaces

Answer 55

the tendency of a surface to appear the same colour despite variations in the colour of illumination - changes in lighting conditions Achieved by discounting the illuminant and determining the true colour of a surface regardless of how it appears Illuminant: the light that illuminates a surface— is not constant Explanations; Memory—common objects have a known colour regardless of illumination Chromatic adaptation—exposure to a particular wavelength of light decreases sensitivity to wavelengths similar to it Comparison to surroundings—factor out illumination by using a ratio principle Other Assumptions; Qualities and position of the illuminant and Directions, orientations, and shapes of surfaces

Answer 56

Retinex = Retina + Cortex The rods alone are capable of lightness constancy The Retinex Theory suggests that each cone engaged in an independent lightness constancy process independent of the other cones Once combined, these three independent values encoded the determinate colour of an object surface

Answer 57

The physiology of the retina does not support the Retinex theory Information does leave the eye in three pathways. But the three pathways do not correspond to the three cones

Answer 58

regular vision have all three types of cones and can distinguish a wide range of colours

Answer 59

wavelength and intensity

Answer 60

it fires more or less

Answer 61

no concept of univarience explains lack of colour in dim lighting - cause there is only a single rod we can detect differences because we have more than one kind of photoreceptor

Answer 62

Memory – common objects have a known colour regardless of illumination ▪ Chromatic adaptation – exposure to a particular wavelength of light decreases sensitivity to wavelengths similar to it ▪ Comparison to surroundings – factor out illumination by using a ratio principle ▪ Other Assumptions ▪ Qualities and position of the illuminant and ▪ Directions, orientations, and shapes of surfaces

colour perception Flashcards

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