Sensation: wavelength

Perception: hue

S: purity

P: saturation (white light really unsaturated)

S: amplitude/intensity

P: brightness (dark or light red)

-white light is the highest amplitude & brightest

Ppl prefer sun bc of diff in distribution of light waves

-standard light has more long wavelengths

-sun light has more short wavelengths

Help understand color vision theories

spectral wavelengths: solid line around edge

middle is more saturated

-adding more white light

-e.g. blue is on outside and as you move in and add white you get baby blue then light gray

AKA color solid: 3 dimensional

1. hue (perimeter of circle)

2. saturation (radius of circle)

3. sensation of amplitude/perception of brightness

top is whiter/brighter

bottom is dimmer/darker/black

Top has more light reflected

bottom has more light absorbed

(black absorbs all wavelengths and none are reflected back to your eye)

Vision is a synthetic sense: everything mixes together (see purple, not 2 diff waves)

diff from audition which is analytic

Pointillism: art made using discrete dots of pigments, when you loook from a distance they all blend together

Top portion has beams of light creating additive mixture

-reflected light

Bottom portion has dyes, pigments, & color filters that are creating subtractive mixtures

-absorbing light

-we can't see absorbed wavelengths

-unpredictable and often diff from additive mixtures

Done with beams of light

Complementary Hues: 2 sets of wavelengths across from each other on wheel (Set 1=blue/yellow, Set 2=green/red)

-you see achromatic when complementary colors are mixed (gray), no bluish yellow or redish green

Uncomplementary hues: mixing any set of colors that aren't complementary

-you see mixture of both colors (eg bluish green)

uncomplementary hue mixtures can create metamers

-2 different sensations that give us the same perception

Yellow panel w/ white light shined on it

-absorbs short wavelengths (violet/blue) and we see other colors not absorbed

Blue panel- subtracts out yellow, orange, & red (long waves)

mixture of blue & yellow subract out yellow, organe, red, blue, violet (see green)

Developmed from color wheel studies, theories aobut how the photoreceptors work

trichromatic theory

Original theory: red, green, & blue-receptors detect only one of the colors

Revised: short, medium, & long sensitive cones

Spectral sensitivity: receptors respond to a range of spectral sensitivity (not just one wavelength)

Rushton

-identified long and medium wavelength sensitive cones in humans

-shined a certain wavelength on the retina

-measured what he got back (nothing send back meant cones absorbed and could detect it)

-found L and M sensitive cones

-coudn't find S bc there aren't very many of them (only 5-10%)

Used microspectrophotometry- used light beams from the visual spectrum and measured how much was reflected off of receptor (not absorbed or detected)

Used dissected retinal tissue from primates

-confirmed M & L and identified S

In some ppl M and L are equal, others have way more L than M

Everybody has less S cones (only 5-10%)

S cones: Max 420 (400-540), no yellow, orange, red

M Cones: Max 530 (400-670), no red

L cones: Max 560 (400-700)

Hering's Opponent Process Theory

• based off of oponent process of complementary hues
• incompatible w/ trichromatic theory
• Antagonism between colors
• red/green, yellow/blue, black/white
• cells increase activity for some wave lengths but are inhibited with others
• doesn't hold at receptor level, true at bipolar and above

Antagonistic center-surround

S cones get opposing input from M & L

M get opposing input from L

L get opposing input from M

(S doesn't oppose bc there aren't enough of them and they aren't strong enough)

+M/-L = activation for med waves

shine 500 on receptive field and +M will activate while -L will inhibit

M cones make larger response bc they are more sensitive to the wavelength

-we will see whole stimulus as green

-M/+L = no activation for  med waves

Shine white light, neither will win out bc neither is more sensitive and they will fire equally

+S/-ML = no firing for short wavelengths

-S/+ML=activation for short wavelengths

Only the S part will respond the short wavelengths

+L/-M = activation for long wavelengths

-L/+M =inhibition for long wavelengths

(L are the only ones that make a response because they are the only ones sensitive at this long wavelength)

• Normal trichromat: typical 3 cone system, normal color vision
• Anomalous trichromat: most common deficiency
• have all 3 cones but spectral sensitivity of one type is atypica
• Dichromat: only have 2 types of cones (1 is missing)
• monochromatic: no cones, usually legally blind (20/200) bc rods have bad acuity
• really sensitive to light, difficulty holding the eye still

protanomalous: L cones are abnormal, insensitive to red/green

deuteranomalous: M cones are abnormal, insensitive to red/green

tritanomalous: S cones are abnormal, insensitive to blue/yellow

protanope: L cones are missing, insensitive to red/green

deuteranope: M cones are missing, insensitive to red/green

tritanope: S cones are missing, insensitive to blue/yellow

more common in males (8%) than females (.4%)

-genetically linked to X chromosome

-except tritanope which isn't linked to X and occurs equally in males and females

Perception of hue is affected by factors other than wavelength (seeing a hue when you shouldn't occording to the wavelength)

1. Simultaneous color contrast: appearance of a hue changes because of another hue present at the same time
2. successive color contrast: appearance of a hue cause by another hue previously presented

• Negative after image: appears after and is the opposite/negative or original image (2 types)
• Chromatic adaptation/after images: decreased response to a wave that is continuously present (colors, red/green blue/yellow)
• Achromatic adaptation/after images: negative after image w/ black and white, no ind hues
• Positive after image: flashes after a pic is taken

+L/-M at basal, L is activating and M is inhibiting bipolar

• then present 670 nm and +L is sensitive to it so it activates a lot and -M isnt effected
• if you keep presenting 670 the L code will go into refractory and only M firest at original basal rate so you just see the opposite color
• Results from P pathways

Sensitivity to diff wavelengths shift towards shorter waves as we go from photopic (cone) vision towards scotopic (rod) vision

Occurs in mesopic condition when illumination is midway between optimal for cones and optimal for reds (intermediate illumination) so both rods and cones are functioning

present 480 & 600 nm wavelength equal in amplitude under phototopic (high) and mesopic illumination

-phototopic illumination participant perceives as equally bright

-mesopic illumination participant perceives 480 as being brighter then 600

photopic

-only cones are functioning

-cones are equally sensitive to 480 and 600 nm

-we see both as equally bright

mesopic

-both cones and rods are working

-rods have increased sensitivity to shorter (480)

-short appear brighter bc of rods

we use the same color name for an object despite changes in wavelength of of the light illumination from the object

(e.g. same color in night as it was during the day)

Edwin Land

distal stimulus: object as it exists in real world

proximal stimulus: representation of object in contact w/ a sensory receptor

 -used 3 patches of color (red, green, blue)

-used additive & subtractive color mixtures to keep changing the wavelength until he was shining the correct combination so that the different patches were reflecting identical wavelengths

-subjects still perceived the distal stimuli (the original colors) instead of proximal

e.g. see cup across room, proximal is elliptical shape, distal is that it is a cup

causes successive color contrast

-your response to a color is diminished after you view it continuously for a long time