Midterm 2: Topic Colour (Part 1,2,3) Flashcards
Why do we perceive colour?
Signalling information
perceptual organization
object recognition
cultural transmission
aesthetics
what colours do we perceive
visible light
400-700nm
what is monochromatic light also known as pure wavelengths
Extremely narrow band of wavelengths that create extremely monochromatic light
what are reflectance curves
objects reflect a bunch of different wavelengths some stronger than others
Objects have a complex distribution of all the wavelengths across the visible light band
why do white and black have relatively flat reflectance curves
White objects have relatively flat curves because they reflect similar amount of light at all wavelengths
Most black objects hardly reflect any light (~10%)
Vantablack S-VIS
One of the blackest materials that humans can use
what is subtractive colour mixing and what colours does it use.
Subtractive color mixing happens when pigments, dyes, or inks are combined. subtractive mixing works by absorbing (subtracting) certain wavelengths and reflecting others.
Cyan, Magenta, and Yellow
what is additive colour mixing and what colours are used
Additive color mixing occurs when different wavelengths of light are combined. This is the primary method used in screens, projectors, and digital displays
red, green and blue
what is colour space?
a way to describe the full range of colours by using a 3D colour space that involves hue, saturation and value
how many colours can humans discriminate
2 million
what is hue
The “chromatic” or rainbow color
what is saturation
The amount of white added to the hue
what is value
How light or dark the color is
what are 2 other versions of colour space
HSL – you’ve got a single scale from very black to very pure color to very white. the other dimension (saturation) is sort of how gray things are going from sort of intense white or intense black to neutral gray
RGB – If you’re working with a computer, given that the way it actually displays color is by how much it turns on a red subpixel, a green subpixel, and a blue subpixel
what is the Inverted Spectrum Argument
The Inverted Spectrum Argument is a philosophical thought experiment suggesting that two people could experience colors differently while behaving identically, challenging functionalist theories of mind and highlighting the problem of subjective experience (qualia)
what is the trichromatic theory
Color perception is based on 3 principal colors
Color perception is based on 3 receptor types
Color perception is a 3-dimensional construct
Trichromatic Theory and color matching experiments
Participant attempts to match test field by adjusting the brightness of lights shining on comparison field
Exactly 3 lights of different wavelengths are necessary to match all test field colors
what are the 3 cone types
S, M and L
what is metamerism
Two different stimuli are perceptually identical
The pattern of activation for the cones are identical so the 2 colours will look the same to us even though the actual wavelength might be different
what is the opponent process theory
Color perception is based on 4 primary colors
Color perception is based on 3 opponent mechanisms
Color perception is a 3-dimensional construct
what colours are in opposition of each other
red and green
blue and yellow
black and white
can never see both opposing colours at same time (something can look reddish or greenish but not both)
what are complementary afterimages
occur when you stare at a colored object for an extended period and then look at a neutral surface, causing you to see the opposite (complementary) color.
This happens due to color fatigue in the photoreceptors of the eye.
what is hue cancellation experiments
The goal is to find out how much of one color is needed to “cancel out” another using the opposing colours
Wiring receptors together to create opponent cells
Signals from cones are combined in opponent pairs through excitatory (+) and inhibitory (-) connections.
This allows for some cells to be excited by one colour and the opposing colour being inhibited
how does Trichromatic & Opponent-Process Theories work together
understand them as explaining different steps in the overall processing of color.
The trichromatic theory captures the representations at the level of the receptors and the opponent process theory explains how we perceive color as opposing pairs
how does context influence colour
Context around a colour seems to influence how we perceive them
We can get the same activation of the cones but the context the colour is in changes and therefore we interpret the colour as different from one another
Context is used to infer wavelengths of illumination
Illumination versus reflectance
- Reflectance → How the object reflects light
- Illumination → How light falls on the object
what is lightness constancy
We tend to perceive whites, grays, and blacks as constant under varying illumination
lightness = gray, black and white
what is ratio principle
Under even illumination, the ratio of reflected light guides perception of lightness
how do shadows impact lightness constancy
The soft edges of shadows indicate illumination edges
Remove shadows and the illusion goes away
Illumination edges versus surface edge
Cues including penumbra of shadows and orientation of surfaces guide the distinction between:
Illumination edges: same surface, different illumination
Reflectance edges: different surface, same illumination
Surface edges are the physical boundaries of objects. illumination edges are caused by changes in lighting that affect how we perceive the object’s brightness or color
what is colour constancy
We tend to perceive objects with the same reflectance as having the same color under varying illumination
perceive color of object as constant even when lighting changes
what is chromatic adaptation
the ability of the visual system to adjust to changes in lighting conditions, ensuring that colors appear relatively constant even under different light sources.
Receptors for a color fatigue/adapt after continuous stimulation
how does memory impact colour (top-down process)
Our past prior experiences and the knowledge based on experience about the typical color of an object seem to be having an influence on your perception of color.
pathway in visual system
Starts at the retina
LGN is in the thalamus and has cells that are sensitive to colour
V1 has colour specialized cells called blobs
V4 is very important for colour perception
ventral or dorsal pathway for colour
Colour perception is done through the ventral pathway and it helps identify WHAT something is
LGN and colour
Has center surround receptive fields that are colour specific
colour and V1 blobs
There are adjacent cells that will be complete opposite to one another for what excites and inhibits them
colour and v4
V4 is a higher and more subjective level of colour perception
Lesion can cause cerebral achromatopsia (cortical color blindness)
Cortical blindness means that your eyes still work, but that the damage to your brain is preventing you from seeing colour (nothing wrong with your eyes)
Ishihara Plate
a widely used color vision test designed to detect red-green color blindness.
The test consists of a series of plates with colored dots forming a number or pattern, which can be difficult to distinguish for individuals with color vision deficiencies.
Typical trichromatism
Have all 3 cone types
Allows us to see all wavelengths of visible light (400-700 nm)
The most common
Monochromatism
Only have rods, no cones (or one cone type)
Can still have information about illumination (dark and light) but have no information about the frequency of wavelength
Called congenital colour blindness
Frequency of occurrence ~1/100 000
Dichromatism
Missing one cone type
Protanopia
type of Dichromatism
Missing L-cones
Produce a red/green deficiency
~1/100 (males)
~1/5,000 (females)
Deuteranopia
type of Dichromatism
Missing M-cones
Produce a red/green deficiency
~1/100 (males)
~1/10,000 (females)
Tritanopia
type of Dichromatism
Missing S-cones
~1/50,000 (males)
~1/100,000 (females)
why is Dichromatism more common in males
Because some genes related to cones are on the X chromosome
Male sex (XY) only has one chance to get a typical copy and female sex (XX) has two chances to get a typical copy
Anomalous trichromatism
Have all 3 cones types, but one of the opsins is slightly different than normal
Also more prevalent in males
Protanomaly
type of Anomalous trichromatism
Malfunctioning L-cones
Deuteranomaly
type of Anomalous trichromatism
Malfunctioning M-cone
Tritanomaly
type of Anomalous trichromatism
Malfunctioning S-cone
Tetrachromatism
3 typical ones (L, M, and S cones)
1 anomalous one
Tetrachromats can see more colors than a typical trichromat, perhaps ~100 million distinct colours
Theoretically have a 4-dimensional color space
Would require 4 colors in order to match all stimuli in a color-matching experiment
Some pairs of stimuli which are metamers for typical trichromats would look different to a tetrachromat
