L2 Light and colour Flashcards
trichromat theory
three cones RBG which all combine different saturations and intensities to give all colours
saturation
red = pink
evidence for the trichromat theory
3 types of dichromacy
protanopia
missing the long cone
deuterenopia
missing M cone
tritanopia
missing the small cone
opponent theory
b/y r/g b/w cones
opponent theory evidence
colour after effects - dichromats lose colours in pairs - people pick out yellow as a true colour
dual processes theory
Retina =trichromat theory. LGN = opponent theory
Light constancy
we perceive objects as the same lightness despite changes in lighting conditions (changes in sensation but not perception).
luminance
the amount of light reflecting of an object
= I*R
illumination
the amount of light emitted by a light source
reflectance
the proportion of light being reflected from an objects surface
we consciously receive information about
reflectance only
adaptation theory
(rejected) as we move from light to dark conditions our visual system becomes more sensitive (photo adaption doesn’t happen that quickly)
unconscious interference theory
we use previous knowledge to estimate illuminance (we are crap at estimating illumination)
relational theories
we use ratios to determine luminance - as illuminance changes the luminance ratio stays the same. There is experimental evidence for these.
retinex theory
we ignore gradual changes in luminance and instead focus on the sharper changes as these indicate signifiant features such as shadows and plane changes or a new object. absolute luminance isn’t very important to us
problems for the relational theories
- scaling (solved by the anchoring heuristic) 2. illuminance edges
Anchoring heuristic
we use the thing of highest luminance in the visual field and mark this as white. everything else is scaled around this.
fuzzy heuristic
illumination edges are less sharper than reflective edges
planarity heuristic
reflectance edges are often coplanar
ratio magnitude heuristic
the luminance ratio in the reflective edges is usually smaller
colour constancy
can cause us to see two objects as the same colour despite same wavelengths, or vice versa
illumination spectrum
(colour) how much light emitted from each frequency -
- natural light has a much more even ill spectr.
although we don’t use background luminance for light constancy
we do use background wavelength for colour constancy
colour constancy
-we use colour memory (can cause after effects like blue bananas). and background wavelength
V1
Absolute colour - changes to background lumination cause changes in firing pattern
v4
perceived colour - background changes doesn’t change the firing pattern
v8
colour after effects
which areas respond better to colour than black and white
v1238
cerebral achromatopsia
intact visual system - patients cannot perceive colours but can discriminate wavelengths (as shades of grey). - have access to wavelength information but cannot see colour
