w10 vse colour vision Flashcards
(22 cards)
what is the basis of colour vision??
colour vision is based on the way light interacts with the eye and brain, not on the physics of light itself, it involves neural processing of diff wavelengths of light which are perceived as colours
why is colour vision useful??
it helps with detecting object borders, distinguishing bet objects 9e,g, fruit and foliage), i dentifying ripe fruits, social communication and modern-day information processing
what are the 3 perceptual dimensions of colour??
hue -> corresponds to the wavelength of light
saturation -> corresponds to the spectral purity
brightness -> corresponds to the physical intensity of light
what types of receptors are in the human eye and what are their funcitons??
human retina contains
rods for vision in dim light, without colour
cones for colour vision
what are the 3 types of cones in the retina??
S cones (blue,~430nm)
M cones (green, ~530nm)
L cones (red,~560nm)
What is the Principle of Univariance in colour vision?
The Principle of Univariance states that each photoreceptor can only respond to light intensity, not wavelength. This means that a single receptor can’t distinguish between intensity and colour (wavelength).
How many types of photoreceptors are needed for colour vision?
At least two types of receptors are needed to distinguish colour. Humans have three types of cones (S, M, and L cones) for colour vision, allowing us to discriminate between different wavelengths.
What is trichromacy?
Trichromacy is the theory that humans have three types of cones (S, M, and L), each sensitive to a different range of wavelengths, which allows us to perceive the full spectrum of colours.
How do colour displays (e.g., TV and screens) use colour mixing?
Modern displays rely on mixing three primary colours (red, green, and blue) to create a wide range of colours. This is based on the concept of trichromacy.
What are metamers in colour vision?
Metamers are different light distributions that, when mixed, appear identical to a human observer. This shows that colour perception is based on the combined output of the three types of cones.
What is colour deficiency(blindness), and how does it affect colour vision?
Colour deficiency (colour blindness) occurs when one or more cone types are missing or malfunctioning. It leads to difficulty in distinguishing certain colours, with types including protanopia, deuteranopia, and tritanopia.
what cones are each type of colour vision missing??
Protanopia: Missing red cones.
Deuteranopia: Missing green cones.
Tritanopia: Missing blue cones.
What is the opponent theory of colour vision?
The opponent theory suggests that colour vision involves three opponent channels:
Red-green: Red is opposed to green.
Blue-yellow: Blue is opposed to yellow.
Black-white: White is opposed to black.
This explains why we can’t perceive “greenish-red” or “blueish-yellow.”
What are opponent colours, and how do they relate to colour vision?
Opponent colours are pairs of colours that cannot coexist in perception, such as red vs. green or blue vs. yellow. The opponent channels process these colours separately, which helps explain colour perception.
What is chromatic adaptation?
chromatic adaption is the visual system’s adjustment to lighting conditions
For example, if you look at red light for a long time, when you look away, you might see green (the opposite color). This happens because your eyes are trying to balance out the red light you were staring at.
what is colour constancy??
colour constancy is the perceptual phenomenon where the colour of an object remains constant despite changes in lighting, the brain adjusts for lighting to maintain a consistent appearance of colours
What is the role of the luminance channel in colour vision?
The luminance channel processes the combined outputs of the L, M, and S cones to detect brightness (white vs. black).
How are colour responses processed in the human visual system?
Colour responses from the cones are processed by three opponent channels:
Luminance channel: Combines all three cone types (L, M, S) for brightness.
Red-green channel: The difference between L and M cones signals red vs. green.
Blue-yellow channel: The difference between L/M cones and S cones signals blue vs. yellow.
How does the red-green channel work in the visual system?
The red-green channel processes the difference between L and M cone outputs, signaling red or green, but not both at the same time.
How does the blue-yellow channel process colour information?
he blue-yellow channel processes the difference between L/M cones and S cones to distinguish blue from yellow, but never both at the same time.
Does the trichromatic theory fully explain human colour vision?
No, while the trichromatic theory explains colour vision based on three cone types, it doesn’t account for opponent colours, the inability to perceive certain colour combinations, or the process of colour adaptation.
where would a spectral sensitivity curve for rods peak??
the curve peaks at 498-500nm where rods are most sensitive (to blue-green light) meaning rods are less sensitive to colours like red (longer wavelengths) and violet ( shorter wavelengths)
