PSY280 - 6. Colour

Question 1

Color

Answer 1

not physical property, but it’s related to a physical property (wavelength)
diff wavelengths of light are interpreted by system as diff colour

Question 2

Color

Answer 2

words we use to describe colour evolves over time
every culture/language, 1 colour emerges first - red
as language evolves, more colours identified
blue last colour, not much in nature is blue - we just collectively call the sky blue

Question 3

Color

Answer 3

colour not actually a physical property, just related to one
result of interaction betw stimulus + nervous system
rats just interpreting wavelengths differently we do
wavelength of light reflected is a property

Question 4

function of color: signaling

Answer 4

tell diff betw safe food/rotten food - food safety
illness can be expressed as changes in colour of skin
traffic lights

Question 5

The function of color: perceptual organization

Answer 5

allows us to perceptually separate objects

facilitate finding fruit

Question 6

The function of color: object recognition

Answer 6

to identify objects
association betw colour + object
changing colour messes with object identification
typical colours/atypical colours/black + white: effects for reaction time + accuracy for object recognition

Question 7

Achromatic colors

Answer 7

experienced when light is reflected equally across the spectrum.

Question 8

Chromatic colors (hues)

Answer 8

experienced when light is selectively reflected – when some
wavelengths are reflected more than others
experience green, some wavelengths of blue reflected
yellow: represented at 570 - yellow, actually has long wavelengths

Question 9

translate physical wavelengths - perception of colour

Answer 9

3 problems:

1. Detection
2. Discrimination: we have to be able to tell diff betw wavelengths
3. Appearance (constancy): assignment need to go with certain objects + not change in different lighting conditions

Question 10

Rods

Answer 10

one kind of photopigment (rhodopsin protein + retinal)

detection of light in the eye by wavelength

Question 11

Cones

Answer 11

1 of 3 kinds of photopigments (“opsins” + retinal).
they vary based on the opsid
rhodopsin, diff opsin but same retinal

Question 12

Opsin

Answer 12

determines spectral sensitivity of photoreceptor

dictates which wavelengths is strongly activating

Question 13

relative proportion of light absorbed vs wavelength

Answer 13

It’s combo of sensitivities that gives
us the visible spectrum
diff absorption spectrums - diff wavelengths absorbed effectively
peak sensitivities of 3 cones roughly correspond to blue, green, red
in terms of short, medium, and long wavelengths

Question 14

S-cones

Answer 14

5–10%

none in fovea- fovea not sensitive to this wavelength

Question 15

M-cones

Answer 15

~30%
more in fovea
531 nm
sensitive to range of wavelengths
green: each stimulated to some degree, M is just stimulated the most

Question 16

L-cones

Answer 16

long
~60%
more in fovea
L-cones: 558 nm

Question 17

discrimination of color

Answer 17

Each photopigment sensitive to a range of wavelengths.

response strength varies for diff wavelengths of the same intensity

Question 18

discrimination of color

Answer 18

pattern of activation important in discriminating colour
response curve for single photoreceptor
light presenting to photopigment same intensity, only thing varies is wavelength

Question 19

The problem of univariance

Answer 19

output of a single photoreceptor is
completely ambiguous
any mix with properly adjusted wavelengths

Question 20

The problem of univariance

Answer 20

H

Question 21

Trichromatic Theory

Answer 21

it’s all relative

Color vision depends on 3 different receptor mechanisms (cones)

Question 22

Trichromatic Theory

Answer 22

s cone response: 450 nm big/625 nm absent
m cone response: 450 nm moderate/625 nm moderate
l cone response: 450 nm smaller/625 nm big

Question 23

Trichromatic Theory

Answer 23

Diff wavelengths of light produce a unique pattern of activation for 3 cones.
mess with intensity, response size will change, but relationships will not.
relative proportion will stay the same regardless of the intensity

Question 24

Trichromatic Theory

Answer 24

light we perceive as orange 625
stimulating L cone, M-cone 70% of response of L cone
blue: s cone response big, m-cone moderate, l-cone small
each colour elicits 3 levels of activation for each cone

Question 25

Trichromatic Theory

Answer 25

Newton (1666): color not a physical property of an object, but in the light. sunlight can be split into discrete components diff components make up the diff colours white light contained all wavelengths

Question 26

Young-Helmholtz Theory

Answer 26

Using color matching technique, Young (and Helmholtz) found that 3 mixing lights are needed to match any reference light.

Question 27

Metamers

Answer 27

``` Physically diff mixtures of wavelengths that look identical. M-Cones L-cones red light 40 units 80 units green light 80 units 40 units total 120 units 120 units yellow light 120 units 120 units ```

Question 28

Metamers

Answer 28

relative pattern of activity that cause perception of colour now we know the mechanisms are the cones perception is combo of activation across conetypes level of activation from right combo is going to be the same as when you present 1 wavelength if pattern of activity is the same = experience is going to be the same

Question 29

Metamers

Answer 29

TV only emits blue, red & green light. What about yellow?: as long as you can match the pattern of activation then you can match the perception

Question 30

Metamers

Answer 30

Pass white light through a yellow” filter: filter that absorbs short wavelengths. TVs use trichromatic pixels: each pixel has g, b, r - get yellow by activating g+b

Question 31

additive color mixing: mixing light

Answer 31

Perceived color depends on wavelengths reflected S - blue, M - green, L - red, M+L - yellow, L+M+S - white when combined together, all wavelengths are reflected we add together wavelengths to predict final perception

Question 32

additive color mixing: mixing light

Answer 32

colour wheel: combo of 2 wavelengths perception can be predicted by colour in the middle nonspectral colours: don’t appear in wavelengths - purple + brown

Question 33

subtractive color mixing: mixing paints

Answer 33

mixing blue + yellow paints blue paint: S reflects all, M reflects some, L absorbs all yellow paint: S absorbs all, M reflects some, L reflects some blue + yellow paint: S absorbs all, M reflects some, L absorbs all

Question 34

subtractive color mixing: mixing paints

Answer 34

when you mix paints, fewer wavelengths get reflected so only ones reflected are those reflected by both subtract out what isn’t reflected by both

Question 35

Reflectance Curve

Answer 35

produce additive colour mixing with paint through pointilism | could produce small points of paint + produce colours not on face, but at a distance would produce flesh colour

Question 36

appearance of color

Answer 36

Using relative activity of 3 types of cones, we can discriminate more than 26000 colors. Physically, colors are distinguished based on hue, saturation & brightness.

Question 37

appearance of color

Answer 37

saturation: amount of hue present - varies from outside to inside diff hues outside boundary of wheel brightness: physical intensity of light reddish green is not possible - more like brown

Question 38

after images

Answer 38

due to adaptation Herring made 2 observations 1.When we assign objects or surfances a color, some combinations of colors are never used.

Question 39

after images

Answer 39

Adaptation to colors produces afterimages which reflects polarity of colour combination suggested alternative interpretation

Question 40

Opponent Color Theory

Answer 40

Perception based on 3 mechanisms (receptors) each based on opponency betw colors: b+w, r+g, b+y observing how ppl behaved- phenomenology 1700s, not until 1960s that we found proof

Question 41

Opponent neurons

Answer 41

(retina, LGN,V1) show an excitatory response to one color and an inhibitory response to its opponent color.

Question 42

Opponent neurons

Answer 42

at the level of the retina, LGN + V1 centre surround organization a) single-opponent: suppressed activity as green surround is activated + no red centre b) red surround reduces inhibition + excites centre best: when whole cell is bathed in red - excites whole centre + none of surround

Question 43

Opponent neurons

Answer 43

Activity in opponent neurons is relative to baseline: compare R/G activity over whole visible spectrum. organization can change, but colour combo doesn’t change gradual change instead of step function

Question 44

Opponent neurons

Answer 44

blue stimulates g a little bit, but green stimulates it maximally yellow stimulates some of red which decreases activation, but red suppresses it (negative threshold) changes as smooth curve as you vary wavelength presented

Question 45

Adaptation

Answer 45

reduction in firing rates of neurons with continued application of a stimulus: adapt to green light white has all wavelengths

Question 46

Adaptation

Answer 46

``` green response” is reduced due to adaptation red is ok, so white minus green looks red neuronal fatigue: neurons get tired B+/Y-: high response for S, small response for M+L ```

Question 47

So is color perception based on the trichromatic theory or opponent process theory?

Answer 47

It’s both! | both but operate on diff levels

Question 48

Convergence

Answer 48

Convergence of excitatory & inhibitory inputs from photoreceptors produces opponency. M + L connected to cell can create opponency Y is combo of M+L wavelengths: M+L feed into Amecrine cell which feeds into retinal excitation of Amacrine inhibits retinal cell

Question 49

constancy

Answer 49

A purple cup looks purple under different lighting conditions despite interactions between illumination & properties of the cup!

Question 50

constancy

Answer 50

If only one wavelength is available for reflection, everything will appear that color. interaction betw illumination + properties of object (wavelength most reflected) most lighting conditions include more than 1 wavelength constancy breaks down because only violet light is reflected

Question 51

color constancy

Answer 51

tendency of a surface to appear the same color under a fairly wide range of illuminants. purple = short + long wavelengths reflected how the cup appears also a function of illuminance sunlight is pretty equal reflection skylight: lots of S, less of M + L curves generated by purple cup are diff, output is diff, but we still perceive it as purple

Question 52

Chromatic Adaptation

Answer 52

Skylight is rich in short wavelengths, your eye adapts to short wavelengths, decreasing your sensitivity to short wavelengths. neuronal fatigue specific to illumination present Skylight: S wavelengths are going to adapt because lots of S pattern of activation becomes more similar, not identical (not a perfect system)

Question 53

Effects of the surrounding

Answer 53

Illumination of colored objects changes in a relative manner. none of surfaces will reflect L because it’s not there to reflect apples will reflect the most of those very little L wavelengths presented nonred are reflecting none of the few L wavelengths

Question 54

Brightness

Answer 54

changes across shadow boundaries, hue does not. as long as hue doesn’t change across brightness changes because side is a shadow, 2 cubes interpreted differently in diff illumination

Question 55

Memory Color

Answer 55

People know the color of familiar objects. asked to reduce the chromaticity until it matched background (gray) participants made banana slightly bluish needed to overcompensate fight the memory colour to produce the opponency

Question 56

Light Constancy

Answer 56

we see whites, greys & blacks as staying about the same shade under different illuminations. ratio principle solves this problem

Question 57

Light Constancy

Answer 57

Of the total light striking an object, an object’s reflectance is the proportion of light that the object reflects into our eyes. ‣black: 5-9% (9/100 or 900/10,000) ‣gray: 10-70% ‣white: 80-95% (90/100 or 9,000/10,000)

Question 58

Light Constancy

Answer 58

under low lighting: less light reflected, but ratio of reflection is still the same with high key lighting proportion stays the same in both illumination

Question 59

Ratio Principle

Answer 59

As long as the ratio of reflectance for the object and its surrounding remains the same, the perceived lightness will remain the same. works best in uniform lighting condition our typical experience is variation in illumination

Question 60

(a) vs. (c) = reflectance edge | (a) vs. (b) = illumination edge

Answer 60

a is reflecting more light than c - a is lighter than c edge betw 2 areas where reflectance betw 2 surfaces changes border betw 2 areas created by diff light intensity in the 2 areas

Question 61

information in shadows

Answer 61

penumbra is the fuzzy border of shadows. bottom up reasons we can tell diff betw painting + real shadow - penumbra on right image, silhouette is too sharp, cues that it’s a painting

Question 62

Top-down contribution

Answer 62

If we know a piece of paper is folded, our visual system uses that information to interpret change in illumination. if we eliminate top down contribution: look at it through tiny hole ability for colour + light constancy is eliminated

Question 63

Top-down contribution

Answer 63

Lightness can be affected by the way elements are perceptually organized. gestalt property overlay 4 circle, see them as darker if overlay constituted as light vice versa

Question 64

infant color vision

Answer 64

Children can see color within the first 3–4 months of life.

Question 65

Habituation

Answer 65

``` when an animal learns to ignore an uninformative repetitive 50 stimulus. percentage of response from 1st response how it changes with repetitions with repetition animal learns to ignore ```

Question 66

looking paradigm

Answer 66

present colour patches to infants as soon as they stop paying attention you take it away with each repetition decrement in looking time present new colour to see how it compares with test condition

Question 67

looking paradigm

Answer 67

present a diff green/a blue colour patch babies categorize green the same way we do because treat it similarly as 510 480: still some habituation but significantly less - diff category of stimulus

Question 68

looking paradigm

Answer 68

results were replicated even when researchers controlled for the confound. ifferent wavelengths, different brightness different brightness (same wavelengths) different wavelength (same brightness) in original experiment: failed to control for brightness replicated even when controlled