Problem 3 Flashcards
What are the functions of color vision ?
- Signaling function
ex. traffic light red = stop - Perceptual organization
- Object segregation
ex. : finding fruit in forest (crucial to survival) - Recognizing objects
ex. : Banana = yellow
Basic colors
- red
- yellow
- green
- blue
Extraspectral colors
Do not appear in the spectrum
–> brown / purple
Saturation
A colors saturation is changed by adding white
–> this decreases it
ex.: red + white = pink ( less saturated )
How do you create a variety of colors ?
By changing the
a) wavelength
b) intensity
c) saturation
Chromatic color/
Hue
Light reflection is a-similar across the full spectrum
–> some wavelenghts are reflected more than others
ex.: red, green , yellow, blue ( basic colors )
Achromatic color
Light reflection is similar across the full spectrum
–> contains no hue
ex.: black, grey, white
Selective transmission
Only some wavelengths pass through the object or substance of transparency to create chromatic color
ex.: cranberry juice selectively transmits LW light
Additive color mixture
Mixing lights, which involves adding up the wavelengths if each light in the mixture
ex. : yellow light + blue light = white light
- -> reflects the sum of the wavelengths
Subtractive color mixture
Mixing paints, which causes fewer wavelengths to be reflected
–> when mixed, both paints absorb the same wavelengths as when they are alone
–> wavelenghts reflected are those that are reflected by both paints in common
ex.: yellow + blue = green, because both reflect M wavelengths
What are Wavelengths ?
WL are energy
–> colors are created by our perceptual system
Trichromatic theory of color vision
Color vision depends on the activity of 3 different receptor mechanisms
–> describes what is happening at the beginning of the visual system
Young - Helmholtz theory of color vision
Light of a particular WL stimulates the 3 receptor mechanisms to different degrees and the pattern of activity in the 3 mechanisms results in the perception of color
–> each WL is represented in the NS by its own pattern of activity in the 3 receptors
Metamerism
2 physically different stimuli are perceptually identical
Are 3 receptor mechanisms necessary for color vision ?
- color vision is possible with 2 receptor types, but not one
- a person with only one visual pigment can match any WL in the spectrum by adjusting the intensity of any of the WL
–> a second pigment is although needed to distinguish between the WLs independent of light intensity
Color deficiency
Partial loss of color perception
–> associated with problems with the receptors in the retina
Monochromat
Color Blindness
Type of color deficiency in which only one WL is needed to match any color in the spectrum
- -> no functioning cones
- -> sees only in shades of grey
Dichromat
Needs 2 WLs to match all other WLs in the spectrum
- -> experience only some colors
- -> inherited through a gene located on X chromosome (more men are affected, because they don’t have a second X chromosome like women)
Opponent process theory
Color vision is caused by opposing responses
–> happens for blue + yellow ; green + red ; black + white
(some receptor cells might be stimulated by red, but inhibited by green, while others do the opposite)
–> this theory describes events happening later in the visual system
Behavioral evidence for the opponent process theory
Viewing a green (blue) field results in a red (yellow) afterimage and vice versa
Simultaneous color contrast
Describes an effect that occurs when surrounding an area with a color that changes the appearance of the surrounded area
–> this explains afterimages
Opponent neurons
Respond with an excitatory response to light from one part and an inhibitory response to light from another part of the spectrum
–> they are responsible for perceptual experiences like
a) afterimages
b) simultaneous contrast
Why are opponent neurons necessary ?
The firing of opponent cells transmits information about wavelength more efficiently than the information contained in the receptor response
Color constancy
We perceive the colors of objects as being relatively constant even under changing illumination
–> without color constancy the color of an object would depend on how it was illuminated
Tungsten light
WL distribution of a light bulb
–> contains much more energy at long WLs (light appears yellow)
–> decreases your eyes to sensitivity to long WLs due to adaptation to it
Sunlight
contains equal amounts of energy at all WLs (white light)
Chromatic adaptation
Prolonged exposure to chromatic color
ex.: adaptation to red light will selectively bleach LW cone pigments - decreasing sensitivity to it
Memory color
Knowledge about the usual colors of objects in the environment helps us achieve color constancy
Lightness constancy
We see whites/ grey/ blacks/ as staying about the same shade under different illuminations
–> when it occurs it is determined by the objects reflectance
Object reflectance
The proportion of the light that the object reflects into our eyes
Ratio principle
When the ratio of reflectance of the object to the reflectance of surrounding objects remains the same, the perceived lightness will remain the same
–> works best for flat + evenly illuminated objects
Reflectance edge
Edge where the reflectance of two surfaces changes
–> usually du to differing materials
Illumination edge
Edge where the lighting changes
