colour theories Flashcards
trichromatic theory history names in order (4)
Palmer (1777), Young (1802), Maxwell (1856), Helmholtz (1911)
Palmer’s (1777) theory
light composed of 3 differently coloured rays (r,y,b) that move particles on the retina
Young’s (1802) theory
3 types receptors in human eye sensitive to r, g, v; based on colour matching with 3 primaries
Maxwell’s (1856) theory
more colour-matching data supported Young’s theory; 4 more primaries needed
colour matching
-supported Young’s theory
-perception of any colour can be matched by additive combo of 3 primary colours (1 primary can’t be perceptual match to mixture of other 2 primaries e.g. metameric matches)
metameric matches
two lights that look the same but have different wavelength compositions
best primaries for colour matching and why?
red, green, blue cuz far apart in colour space; can be mixed to match broadest range of standard colours
in colour matching, each colour can be uniquely described in terms of
a proportion of the 3 primaries
Young-Helmholtz trichromatic theory
perceived colour of any light is determined by the output of 3 receptor types
physiological evidence of trichromatic theory by Rushton (1960)
found cones that absorb long wavelengths and medium wavelengths
microspectrophotometry
technique for measuring wavelengths absorbed by individual cones
microspectrophotometry physiological evidence for trichromatic theory
found cones absorbing short wavelengths
Photo pigment curves are physiological evidence for
3 primaries needed for colour matching
Why do we need more than 1 type of photoreceptor?
Principle of univariance
Principle of univariance
The response of each photoreceptor only varies in one dimension
What is example of univariance?
Response of photoreceptors only varies in amplitude
T/F: response of photoreceptors can be the same but the wavelengths are different
True, that’s why we need multiple photoreceptors
T/F: output of single photoreceptor is ambiguous which means we need only 1 dimension
False; is ambiguous which means we need 2 dimensions (intensity and wavelength info needed)
what two dimensions are needed to perceive colour?
intensity and wavelength
when 2 wavelengths produce the same response in 1 cone type, the 2 wavelengths ___
produce different patterns of responses across 3 cone types
metameric colour match example
perception of red + green = yellow
is colour discrimination possible in all parts of the spectrum with only 2 types of cones?
no
Opponent process theory history: who’s the main guy?
Hering (19th c., Germany)
Hering’s theory
there are 4 colour words rather than three used to describe sensations (red, green, blue, yellow) that are excited or inhibited
which colours inhibit which colours in opponent process theory?
[B- W+], [G- R+], [B- Y+]
psychological evidence for opponent process theory
complementary hues, complementary afterimages, unique hues
complementary hues vs complementary afterimages
complementary hues cancel out and look grey; complementary afterimages appear after fixating on opposite colours for a while
unique hues
hues that can be described with only a single colour term (red, green, yellow, blue)
cardinal hue
when red-green and blue-yellow axes are in perceptual colour space
hue cancellation also known as
colour nulling
hue cancellation technique is strong psychophysical evidence for what theory?
opponent theory
hue cancellation theory
adjusting proportions of colour to cancel out colour (e.g. cancelling out bluish and yellowish)
T/F: values above the dotted line in the hue cancellation graphs mean that you are cancelling the colour shown with opponent colour
true; yellow line above line means you are adding blue to cancel yellowness
spectral opponency
neuron is excited by wavelengths from one part of the spectrum and inhibited by wavelengths from a different part of the spectrum; also known as colour opponency
physiological evidence for colour opponency
retinal ganglion cells: blue-yellow (bistratified cells; one blue, one yellow); red-green/spatial opponency (foveal midget cells; centre vs surround (4 variations)); midget & parasol for brightness axis
dual-process theory of colour vision (order)
light-> receptors (trichromatic) (detection)-> opponent cells (opponent theory) (discrimination)-> brain
how is trichromatic theory involved in dual-process theory of colour vision?
the receptors participate in colour matching; cones and additive wavelength
how is opponent theory involved in dual-process theory of colour vision?
retinal ganglion cells; afterimages, complementary hues, colour nulling
retinal ganglion cells for red-green channel & related cones (square brackets)?
foveal midget ganglion cells; [L-M] or [M-L]
retinal ganglion cells for yellow-blue channel & related cones (square brackets)?
bistratified ganglion cells (all yellow, all blue); [(L+M)-S] or (S-(L+M))
retinal ganglion cells for achromatic channel (brightness axis) & related cones (square brackets)?
midget & parasol ganglion cells; [L+M]
trichromacy
normal colour vision; 3 cone photopigments; 3 primaries needed for colour matching
anomalous trichromacy
colour deficiency with 3 cone photopigments but 1 is abnormal; abnormal proportions with 3 primaries for colour matching; colour discrimination difficulties
types of anomalous trichromacy (most common to least)
deuteranomaly, protanomaly, tritanomaly
dichromacy
colour deficiency with 1 missing cone photopigment; normal # of cones; 2 primaries for colour matching; neutral point in spectrum where grey perceived
types of dichromacy (most common to least)
protanopia, deuteranopia, tritanopia
monochromacy
rare, total colour blindness, missing 2 or 3 types of cones
types of monochromacy
cone monochromacy, rod monochromacy
difference between anomalous trichromacy, dichromacy, and monochromacy?
number of cones missing and/or abnormal cone photopigment; tri has 1 abnormal, di has 1 missing, mono has 2/3 missing
anomalous trichromacy vs dichromacy morpheme endings for different types within each
anomalous trichromacy: -anomaly
dichromacy: -anopia
all the __-anomaly/-anopia and __-anopia/-anomaly, and cone monochromacy involve X-linked recessive inheritance
deuter; prot
__-anomaly/- anopia linked with autosomal dominant inhertiance, chromosome 7
trit
deuter____ associated with _ cone photopigment
M
prot___ associated with _ cone photopigment
L
trit____ associated with _ cone photopigment
S
deuteranomaly
type of anomalous trichromacy
-abnormal M cone photopigment; more green primary for matching
-genetic mutation in opsin genes (X-linked recessive inheritance)
protoanomaly
type of anomalous trichromacy
-abnormal L cone photopigment; more red primary for matching
-genetic mutation in opsin genes (X-linked recessive inheritance)
tritanomaly
abnormal S cone photopigment; more blue primary for matching; autosomal dominant inheritance, chromosome 7
deuteranopia
-type of dichromacy
-M cone photopigment missing
-neutral point ~ 498nm
-X-linked recessive inheritance
protanopia
-type of dichromacy
-L cone photopigment missing
-neutral point ~ 492 nm
-X-linked recessive inheritance
tritanopia
-type of dichromacy
-S cone photopigment missing
-neutral point ~ 570nm
-autosomal dominant inheritance, chromosome 7
cone monochromacy
-only 1 type of cone (usually S)
-shades of grey
-X-linked recessive inheritance
rod monochromacy
-no cones
-shades of grey
-poor acuity, difficulty with photopic vision
-autosomal recessive inheritance, chromosome 2 or 8
how do inherited retinal colour deficiencies support dual-process theory?
-missing/abnormal photopigments in each type of colour support trichromacy at photopigment level
-neutral points/colours perceived support opponency
neutral points in dichromacy determined by ____ channels
opponent
