212 final Flashcards
cerebral achromatopsia
colour blindness due to brain injury
chromatic colours
selective reflection of light = red, green, blue, etc.
achromatic colours
equal reflection of light (white, black, greys)
spectral colours
in the visible spectrum
nonspectral colours
results of mixing other colours
hues
chromatic colours
saturation
intensity of colour
value
light-dark dimension
trichromatic theory (Young-Helmholtz)
3 principal colours/receptors with different spectral sensitivities
colour matching
matching a reference colour (only requires 3 wavelengths)
microspectrophotometry
determining absorption spectrum by directing a beam of light at a specific receptor
metamerism
different stimuli create the same perceptual experience (colour matching)
monochromatism
no functioning cones = only rods (shades of grey), intensity of light can help differentiate between WLs (number of photons)
- if photons in a wavelength are altered, you can create the same perception
principle of univariance
once isomerization has occurred, the wavelength loses its identity (only the amount of energy is known by the receptor)
photons
small packets of energy in light
dichromatism
ratio of response in two pigments (confuse some spectral colours), diagnose with ishihara plates
protanopia
missing long wavelength pigment, neutral point is 492 nm = blues to yellows
deuteranopia
missing medium wavelength pigment, neutral point is 498 nm = blues to yellows
tritanopia
missing short wavelength pigment, neutral point is 570 nm = blues to reds (without green)
neutral point
wavelength at which colour is so desaturated it is perceived as grey
anomalous trichromatism
wavelengths are mixed at different proportions to match a colour (trouble differentiating wavelengths that are close to each other) - pigments have different absorption spectra
opponent-process theory of colour vision
opponent neurons in the lateral geniculate nucleus create colour vision by causing opposing responses blue-yellow and red-green
phenomenological evidence for opponent-process theory
hue scaling experiments - the four ‘pure’ primary colours which weren’t created by mixing other wavelengths
psychophysical evidence for opponent-process
hue cancellation experiments - yellow could be added until the ‘blue’ perception disappeared
physiological evidence for opponent-process
opponent neurons found in monkeys’ LGN
- circular single opponent (for large areas of colour)
- circular double opponent (for borders and patterns)
- side-by-side opponent (for large areas of colour)
colour constancy
colours appear constant no matter what the illumination is
chromatic adaptation
after prolonged exposure to a wavelength, cones become less sensitive to it = those colours appear less saturated
creates partial colour constancy
partial colour constancy
when one is adapted, the colour perception is less different than unadapted (in a red-lit room, the colours of objects remain constant because LWL cones are adapted and respond less to LWLs)
memory colour
familiarity of objects contributes to colour constancy (appear more saturated) - yellow bananas, red stop signs
illumination
amount of light striking an object’s surface
reflectance
percentage of light being reflected off an object into our eyes
lightness constancy
perception of lightness comes from reflectance, not illumination (as long as the percentage of the total amount of light stays the same, our perception stays the same)
reflectance of black
under 10%
reflectance of grey
10-70%
reflectance of white
80-95%
ratio principle in colour constancy
in even illumination, lightness perception is determined by that object’s reflectance compared to its surrounding objects
illumination edge
borders at which lighting changes/we see shadows
reflectance edge
borders at which the reflectance of two surfaces changes
how to differentiate between illumination vs. reflectance edge
shadows have meaningful shapes and have a penumbra (fuzzy borders)
monochromatic light
light composed of a single wavelength
red
long wavelengths 620-700 nm
green
medium wavelengths 500-575 nm