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Color Vision & Deficiencies
Lecture 8 & 9, Exam 2
36
Psychology
Graduate
10/15/2012

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Cards

Term
Sensations & Perceptions in vision
Definition

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

Term
sunlight vs. standard light bulb
Definition

Ppl prefer sun bc of diff in distribution of light waves

-standard light has more long wavelengths

-sun light has more short wavelengths

Term
color wheel
Definition

Help understand color vision theories

spectral wavelengths: solid line around edge

Term
Center of color wheel
Definition

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

Term
Color spindle
Definition

AKA color solid: 3 dimensional

1. hue (perimeter of circle)

2. saturation (radius of circle)

3. sensation of amplitude/perception of brightness

 

Term
amplitude dimension
Definition

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)

Term
Color Mixing
Definition

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

Term
Mixtures on the color spindle
Definition

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

Term
Types of hue additive mixtures
Definition

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)

Term
One effect of additive mixture
Definition

uncomplementary hue mixtures can create metamers

-2 different sensations that give us the same perception

Term
Subtractive mixtures
Definition

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)

Term
Color Vision Theory
Definition

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

 

trichromatic theory

Term
trichromatic theory
Definition

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)

Term
trichromatic theory experiment
Definition

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%)

Term
Discovering S receptors
Definition

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

Term
Amount of M, L, and S cones
Definition

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

 

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

Term
Different cones spectral sensitivity
Definition

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

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

L cones: Max 560 (400-700)

Term
Second visual theory
Definition

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
Term
Opponent Process bipolars
Definition

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)

Term
M/L center surround antagonism
Definition

+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

Term
S/ML antagonistic center surround cells
Definition

+S/-ML = no firing for short wavelengths

-S/+ML=activation for short wavelengths

 

Only the S part will respond the short wavelengths

Term
L/M center surround antagonism
Definition

+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)

Term
Types of Color vision
Definition
  • 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
Term
Types of Anomalous trichromat
Definition

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

 

Term
types of dichromat
Definition

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

Term
Characteristics of color deficiencies
Definition

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

Term
Color Phenomena
Definition

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

 

Term
Examples of successive color contras
Definition
  • 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

 

Term
S cones from a distance
Definition
From far distances you can see red/green, but blue/yellow turn grey bc there are less S cones
Term
After images with receptors & bipolar cells
Definition

+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

 

Term
Purkinje Shift
Definition

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

Term
Purkinje shift experiment
Definition

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

Term
Photopic vs. mesopic conditions explanation
Definition

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

Term
Color constancy
Definition

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)

Term
Experiment for color constancy
Definition

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

 

Term
chromatic adaptation
Definition

causes successive color contrast

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

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