Task 3: Colour Flashcards
“Pure/unique” colors
red, yellow, green, blue - all colors can be described with these
Desaturation
changing color by making light brighter by adding white e.g. red + white = pink
Name the 3 Types of Cone Pigments
S - 419 max - blue
M - 531 max - green
L - 558 max - red
Chromatic colors/hues
(e.g. blue, green, red) occur when some wavelengths are reflected more than others through a process called selective reflection
Selective reflection
objects selectively reflect some wavelength (opaque objects) -> chromatic colours more
Selective transmission
only some wavelengths pass through the object/substance (transparent objects) e.g. cranberry juice
Transmission curves
plots of the percentage of light transmitted vs wavelength
Additive color mixing
mixing lights involves adding up the wavelengths of each light in the mixture
Subtractive color mixture
mixing paints causes fewer wavelengths to be reflected because each paint subtracts wavelengths from mixture
How is black created in relation to subtractive colour mixing
when reflected wavelengths of 2 colors differ, however is rare
Trichromatic theory of colour vision
colour vision depends on the activity of 3 different receptor mechanisms, based on the psychophysical procedure called colour matching
Colour matching experiements
observers adjusted the amounts of 3 different wavelengths of light mixed together in a “comparison field” until the colour matched the colour of a single wavelength in a “test field”
Young-Helmholtz Theory of Color Vision
colour vision depends on 3 receptor mechanisms, each with different spectral sensitivities
- > Light of a particular wavelength stimulates each receptor mechanism to different degrees and the pattern of activity in the 3 mechanisms results in colour perception
- > Therefore, each wavelength is represented in the NS by its own pattern of activity in the 3 receptor mechanisms
How is white formed by receptors?
equal signalling of all 3 receptors
How are cones responsible for 3 different absorption spectra?
the long opsin part of the visual pigments differ
Metamerism
when 2 physically different stimuli are perceptually identical e.g. lights in the trichromatic experiment being physically different but perceptually identical
Metamers
2 identical fields (lights) being perceptually identical but not physically the same, this is due to them resulting in the same pattern of response in 3 cone receptors (2 lights are physically different but when combined look the same)
Isomerization
visual pigment isomerizes (retinal changes shape) when the molecule absorbs one photon of light, this activates the molecule and triggers the process that activates the visual receptor to see light
Color deficiency
partial loss of colour perception, usually due to problems with retinal receptors present at birth
How can color deficiency be determined?
o Colour tests e.g. Ishihara plate
o Using the colour-matching procedure (to determine the minimum number of wavelengths needed to match any other wavelength in the spectrum)
Unilateral dichromat
trichromatic vision in one eye, dichromatic vision in the other (can determine for use what a dichromat sees)
Monochromat
a) how many pigments
b) describe wavelengths
c) visual acuity level
d) colors seen
a) 1 pigment
b) can match any wavelength in the spectrum by adjusting the intensity of any other wavelength therefore needs only one wavelength to match any colour in the spectrum
c) poor, rod system overloaded in strong illumination, sensitive to bright lights
d) white, grey, black
Dichromat
a) how many pigments
b) describe wavelengths
c) name 3 types
a) 2
b) only needs 2 wavelengths to match all other wavelengths in the spectrum
c) protanopia, deuteranopia, tritanopia
Protanopia
is missing the long-wavelength pigment
Deuteranopia
is missing the medium-wavelength pigment
Tritanopia
is missing the short-wavelength pigment
How are protanopia and deutranopia inherited
through X gene on chromosome, females can carry it and not be colour blind but a carrier (XY)
Anomalous Trichromat
Needs 3 wavelengths to match any wavelengths however mix these in different proportions therefore not good as discriminating
Opponent-process theory of color vision
proposed based on behavioural observations (contrasting trichromatic theory based on psychophysical experiments), based onresults of phenomenological observations, in which stimuli were presented and observers described their perception
Simultaneous color contrast
one colour can change how we perceive the tone and hue of another when 2 are placed side by side
3 mechanisms of opponent-process theory of color vision
o Black (-) and white (+) mechanism
- > Responds positively to white light
- > Responds negatively to the absence of light
o Red (+) and green (-) mechanism
- > Responds positively to red
- > Responds negatively to green
o Blue (-) and yellow (+) mechanism
- > Responds positively to yellow
- > Responds negatively to blue
o Physiological research showed that these colours do cause physiologically opposite responses
Opponent neurons
in the retina and LGN, respond with an excitatory response to light from one part of the spectrum and with an inhibitory response to light from another part
Areas for processing…
a) face
b) body
c) place
a) fusiform face area
b) extrastriate body area
c) parahippocampal place area
Cerebral achromatopia
: a condition caused by brain damage, cannot see colour (other effects include prosopagnosia)
Is there a particular region for color detecting in the brain
colour perception results from activity in many different visual areas that respond not only to colour but to other qualities e.g. form
Color constancy
we perceive colours of objects as being relatively constant even under changing illumination (think- green jumper) -> brain corrects
Chromatic adaptation
prolonged exposure to chromatic colour, can change colour perception
Memory colour
knowing the usual colours of objects in the environment -> expectancy effects
Achromatic colors
grey, white, black
Lightness
shade of achromatic colour
Lightness constancy
we see whites, greys, blacks as staying about the same shade under different illuminations
Ratio principle
as long as this ratio remains the same the perceived lightness will remain the same
Ratio of ratio principle
Reflectance of the object : Reflectance of surrounding objects
Reflectance edge
an edge where the reflectance of 2 surfaces change
Illumination edge
edge where lighting changes
3 steps of colour perception
- detection
- discrimination
- appearance (despite changing conditions i.e. constancy)
Electromagnetic energy is produced by ___ ___ and radiated as ___
electric charges, waves
Wavelength
distance between peaks of electromagnetic waves
Reflectance curve
plots amount of light reflected vs wavelength
How are achromatic colours produced?
light is reflected equally across spectrum (white higher percentage of light vs black)
Hue cancellation experiment
aims at seeing how much of opponent colour needs to be added in order to cancel all perception of other colour
Double-opponent cell
visual cortex, one region is excited by one cone type, combination of cones or color and inhibited by opponent cones or colour
Why does colour constancy occur? x3
1 chromatic adaptation
2 effect of surroundings
3 memory colour
Amount of light reaching eye from objects depends on x2
1 illumination
2 reflectance from object
Why does light constancy occur? x2
1 ratio principle
2 perception under uneven illumination
How does visual system distinguish between 2 edges? x 3
Based on
1 shape of the shadow
2 penumbra
3 orientation of surface
