Lecture 4: Colour vision and Perception Flashcards
How does black and white imagery (like old movies) highlight the importance of colour?
Colour enhances our ability to interpret and understand the visual world, such as mood, symbolism, and clarity. Black and white movies lack these visual cues.
What are some uses of colour?
- To interpret the world around us e.g. Providing symbolic meaning (e.g., traffic lights)
- It affects mood
- Helps to interpret food properties e.g. ripeness
- Identifying health signals(e.g., red for oxygenation)
Why is colour important for understanding food properties?
Colour helps infer other properties like ripeness or freshness.
Example: A green banana is hard/unripe, while a yellow banana is ripe.
How does the visual difference between colour and black & white bananas demonstrate the role of colour?
In black and white, all bananas look similar. In colour, ripeness and condition can be identified clearly.
How do baboons use colour as a signal?
A baboon’s red bottom signals readiness to mate.
How is colour used symbolically in everyday life?
Examples include:
- Red and green traffic signals (STOP/GO)
- Red pen for corrections
- Social signals like blushing (red face)
How does colour aid in recognition?
Colour helps locate objects, such as finding your car in a parking lot.
How does colour relate to cultural and social groups?
Colour can represent affiliations, like wearing team jerseys or specific colours for cultural events.
What role does colour play aesthetically?
Colour is used to make objects and environments visually appealing.
How does colour influence social aspects of communication ?
Colour conveys emotions or states, such as blushing (red face) during embarrassment.
Where does colour come from?
Colour comes from visible light—a small portion of the electromagnetic spectrum.
How do our eyes process colour?
Our eyes detect colour through photoreceptors, but colour is constructed by the brain based on detected wavelengths of light.
What are the three types of cones in human trichromatic vision (Human Trichromacy) and what type of light are they sensitive to?
- Short (S) cones – sensitive to blue wavelengths
- Middle (M) cones – sensitive to green wavelengths
- Long (L) cones – sensitive to red wavelengths
What is the role of the cone photoreceptors?
Cones allow humans to perceive colour by detecting different wavelengths of light.
What did the retinal cone mosaic image show?
The mosaic shows a high density of red and green cones (L&M) but fewer blue cones (S).
Why are humans trichromatic? (Regan et al., 2001)
Trichromatic vision evolved to help humans detect ripe fruits against green foliage.
What are the two main cone types in dichromatic vision?
Dichromatic species have:
* Short (S) cones
* Long (L) cones
e.g. dogs, frogs
What did Changizi, Zhang, & Shimojo (2006) suggest about trichromatic vision?
Trichromatic vision helps detect oxygenation levels in blood, which can signal health status through changes in skin colour.
How does oxygenation in blood affect colour perception? (Changizi et al., 2006)
- More oxygen: Skin appears redder
- Less oxygen: Skin appears greener or yellower
Why do trichromatic primates have more bare skin compared to monochromatic or dichromatic species?
Bare skin allows colour signals, like changes in blood oxygenation, to act as socio-sexual signals (Changizi et al., 2006).
How is colour sensitivity distributed in photoreceptors?
Cones are sensitive to specific wavelengths:
* Blue (S): Short wavelengths
* Green (M): Medium wavelengths
* Red (L): Long wavelengths
What did Changizi et al. (2006) find about colour signals across races?
Colour signals related to blood oxygenation are universal across all human races.
How is colour processed in the brain?
Information received from photoreceptors through pathways in the visual cortex.
Where does the Midget (parvocellular) pathway project to in the brain?
It projects to the:
* Primary Visual Cortex (V1),
* V2
* V4 in the ventral stream (temporal lobe).
What is the function of the koniocellular pathway?
The koniocellular pathway processes signals from the blue (S) cones and aids in short-wavelength colour discrimination.
What is the general flow of information in colour processing? (5)
- Photoreceptors (cones): Detect wavelengths of light (S, M, L cones).
- Retina: Signals pass through bipolar and ganglion cells
- Lateral Geniculate Nucleus (LGN): Colour signals are processed.
- Primary Visual Cortex (V1): Initial processing of colour.
- V4 (Temporal Lobe): Higher-level colour perception.
What happens in V4 in the visual cortex?
V4 specializes in colour perception, integrating visual inputs to produce the experience of colour.
Which visual cortical areas relay colour signals between V1 and V4?
Visual area V2 relays colour information from V1 to V4 for higher-level processing.
Which brain lobe is primarily associated with higher-order colour perception?
The temporal lobe, as part of the ventral stream.
What are monochromats and what can they see?
Monochromats have only one cone or rods type only. They can only see lightness and darkness (e.g., black-and-white vision).
What are the three types of dichromacy?
- Protanopia: Lack of L (long-wavelength, red) cones.
- Deuteranopia: Lack of M (medium-wavelength, green) cones.
- Tritanopia: Lack of S (short-wavelength, blue) cones.
What is anomalous trichromacy?
It is a colour vision deficiency where cone sensitivities are shifted:
* Deuteranomaly: M cone is shifted towards L.
* Protanomaly: L cone is shifted towards M.
Why is colour vision deficiency more common in men?
Females inherit the fauly X chromosome, so males (XY) are more likely to inherit since X chromosome is from mother, than females (XX).
How does age affect colour vision?
With age, our lenses become yellower, reducing the input to the S cones (blue light).
What happens to blue and yellow in the colour after-effect?
Blue and yellow swap and appear in a more pastel form.
- focus on black middle dot for 10 seconds then look at the blank, you will see the colour shift.
What are complementary colours in cone opponency?
- Blue is opposed to yellow.
- Red is opposed to green.
How does adaptation in cone opponency contribute to colour after-effects?
Adaptation (staring at the colour tires the cones) reducing sensitivity, creating an afterimage in the opponent colour when looking away due to imbalance in the opponent channels, the brain is balancing the signal.
What are Mondrian patterns?
Mondrian patterns are collections of coloured patches used to study aesthetic responses to colour.
What did Purves & Lotto (2002) demonstrate about colour constancy?
They showed that tiles appearing blue (left) and yellow (right) are actually the same grey colour, but the brain interprets them differently based on illumination.
