color perception (ch 6) - exam 2 (3/3)

1. how photons of light interact with the world (absorption/reflection)

2. what eyes and brains do with the light

2 reasons we see color

newton’s apparatus

putting white light from the sun through a crystal prism resulted in the diffraction of light/a rainbow (ROYGBIV)

• sunlight = composite light

• spectral lights (1 WL) cannot be divided = pure light

composite light

type of light discovered through newton’s apparatus - made up of different wavelengths to produce white light (sunlight)

pure light

type of light discovered through newton’s apparatus - 1 wavelength, a spectral light

• monochromatic

signal and organization/detection

functions of color vision

signal

function of color vision - tells us something about the world

• ex: traffic lights, raw v. cooked

organization/detection

function of color vision - helps with pattern detection

• it’s harder to find patterns in monochromatic (B/W) images than in colored images

absorption

of the three functions of light (absorb, pass through, reflect), this gives objects their color

• grass ____ red and blue to reflect green

reflectance curve

shows what is reflected or absorbed by objects

• achromatic colors: flat in graph b/c they only absorb ALL wavelengths of light, and what we see is the ratio they reflect

  • white: ALL wavelengths are reflected

  • grey: SOME reflected

  • black: LESS reflected

• chromatic colors: selective reflections - reflecting some more than others

spectral reflectance

ratio of light reflected by an object at each wavelength

achromatic colors

flat lines in a reflectance curve - they only absorb ALL wavelengths of light, and what we see is the ratio they reflect

• white: ALL wavelengths are reflected

• grey: SOME reflected

• black: LESS reflected

chromatic colors

other lines in a reflectance curve - selective reflections

• some objects reflect more WLs than others, resulting in how we perceive color

hue, brightness, saturation

color characteristics

hue

color characteristic - the name of a color

• representative in a color wheel with saturation

saturation

color characteristic - paleness/vividness of light

• increased ____ = increased vividness of color

• representative in a color wheel

  • edges: most saturated

  • inner: white

brightness (value)

color characteristic - lightness/darkness

• amount of light present; makes it easier to see color when more present

color terms, color mixing

ways to describe the color experience

color terms

way to describe the color experience - names

• 100s/1000s, but condensed to about a dozen across cultures

habituation and dishabituation

how we know babies can recognize color

• paying attention to a new color/stimulus until it gets old/bored (____)

• when a new color is presented, baby pays attention again (_____)

additive

type of color mixing that lights obey

• combination of WLs reach the eye - making a new color by adding lights together without destroying their individual properties

  • in a pigment: yellow + blue = green

  • in lights: yellow + blue = white

subtractive

type of color mixing that pigments obey

• colors absorb/reflect different wavelengths, so when combined, their middle ground is reflected, thus subtracting out what’s absorbed

  • removal of wavelengths

    • blue reflects shorter WLs and absorbs longer WLs

    • yellow reflects longer WLs and absorbs shorter WLs

      • green = what both blue and yellow reflect

trichromatic theory of color and opponent-process theory of color vision

neural code for color vision (2 theories)

trichromatic theory of color

Young and Helmholtz, 1802 - theory of color vision that proposes that colors can be coded by 3 principle receptors in the eye

• no single type of receptor can give appropriate color vision, resulting in 3 cone systems

• using metamer psychophysical color matching to determine that all 3 primary color lights are needed to match other colors - possible to match all colors in the visible spectrum with an appropriate mix of the three

• CRITIQUE: does not explain afterimages

metamer color matching

part of trichromatic theory of color

• having an individual, in a dark space, match a given patch of color with 3 primary color lights (red, green, and blue)

• task cannot be done with only 2 lights

• possible to match all colors in the visible spectrum by mixing the 3 primary colors appropriately

opponent processing theory

Hering - theory of color vision that proposes that there is a distinct pattern to the color of the afterimages we see with 3 distinct channels

• channels based on complementary colors/opposite sides of the color wheel

  • opponent chromatic channels

    • red/green

    • yellow/blue

  • achromatic channel

    • white/black (light v. dark)

• when processing 1, we don’t see the other, but when the image goes away, there’s an influx from the other end of the channel, resulting in us seeing green after red is flashed

• hue cancellation: can use the channels to cancel out the other’s presence in a mixed color

red/green, blue/yellow, black/white

channels in opponent-process theory

hue cancellation method

Hurvich and Jameson - psychophysical evidence that supports opponent processing theory

• bluish green presented: add yellow to remove the blue and leave green

• can use the channels to cancel out the other’s presence in a mixed color

trichromatic: receptor
opponent process: neural

how do both the trichromatic theory and opponent-process theory explain different aspects of color vision?

monochromacy, dichromacy (protanopia, deuteranopia, tritanopia)

types of color deficiencies

monochromacy

type of color deficiency in which a person has no functioning cones, leading them to only see in black and white

dichromat

type of color deficiency in which an individual is missing 1 cone system, resulting in 2 functioning cones

• three types: protonopia, deuteranopia, tritanopia

protonopia, deuteranopia, tritanopia

3 types of dichromats

protanopia

type of color deficiency in which an individual is missing long WL cones (L-cones)

• reds affected - R/G colorblind

• sex-linked to X chromasome

deuteranopia

type of color deficiency in which an individual is missing medium WL cones (M-cones)

• greens affected - R/G colorblind

• sex-linked to X chromasome

tritanopia

type of color deficiency in which an individual is missing short WL cones (S-cones)

• blues affected - B/Y colorlblind

• NOT sex-linked

protanopia and deuteranopia

sex-linked color deficiencies

L cones, reds

cone system protanopes are missing + corresponding color affected

M cones, greens

cone system deuteranopes are missing + corresponding color affected

S cones, blues

cone system tritanopes are missing + corresponding color affected

tetrachromacy

females with 4 cone systems, resulting in vivid colors/colors we cannot see in their vision

color constancy

in which color perceived the same with changes in WL composition

• ex: inside v. outside, daylight vs. evening light

Young and Helmholtz

pioneers of trichromatic theory of color

hering

pioneer of opponent-processing theory

Hurvich and Jameson

pioneers of the hue cancellation method (which supports opponent-processing theory)