L6 - Motion Flashcards
1
Q
What is wavelength?
A
Wavelength is physical property of light
2
Q
What is colour?
A
Invention of our brain, e.g we see green, but other animals do not
3
Q
What makes up light?
A
- Light has different wavelengths, and visible light is one of these waves, however if we were another animal, their visible light would vary
- Within our visible spectrum, wavelength varies smoothly and evenly BUT our percept of colour does not, the light itself is not coloured but we perceive it like that
- Colour does not follow same rules as light because of our visual system = although wavelengths are smooth, our colours move quickly, we can see more colours at around 580 and 460 nm
4
Q
What is addition and subtraction of light?
A
- Light from sun = white light = made from many wavelengths
- When you add different wavelengths of light = can create other colours
- For colour subtraction, we must use absorption e.g When we see red on a newspaper, it is because all other colours are absorbed
5
Q
What was a study looking at making light?
A
- Place yellow light on one side, then ask a person on the other side to change the lighting with a different colour, and they have to create the same colour as the other colour
- When given 2 torches, you can get some matches but not for most wavelengths of light
- When given 3 torches, can make a perfect match
6
Q
What is the trichromacy theory?
A
- We require three things to match any colour: because we have three types of cones that produce our colour. Many animals do not have 3 types of cones so have a different colour system
- Used in TV sets: any 3 colours will do (there are no primary colours)
- A single wavelength can be perfectly matched by a mixture of three other wavelengths
7
Q
What is colour mixing?
A
Mixing paints results in colour subtraction as each point removes light of particular wavelengths, and newspapers use this technique
8
Q
What are the 4 main photoreceptors?
A
- Green (on diagram) = rods = very sensitive to light= activated by a single photon of light = issue is when you have several, they become a nuisance = only for when there’s not that much light around
- Cones = blue (short) cones, green (medium) cones and red (large) cones but they absorb over a long area of the spectrum
- Common experiment is place electrode and place it in one of these cells and check what wavelengths of light are absorbed and see what it reacts to.
9
Q
What is the principle of Univariance?
A
- Rods cannot tell difference between changes of wavelength and intensity
- Cell can change more/less but world changes on so many dimensions not measured by the cell
- Any stimulus evokes a response whose strength is governed by both intensity and wavelength in a single number (univariant), so stim represent above both give the same response so we cannot see apart
- Animals with only one kind of photoreceptors suffer problems of univariance (can only be resolved by having more than one receptor)
- Likewise a stimulus of 3x the intensity whose percentage wavelength is absorbed is 3x less
10
Q
What is the two receptor system?
A
- Receptors: one short and one long wavelength cone
- The light will activate the two cones differently but at the same time
- Ratio of how the wavelength reacts is different between the two receptors
- Colour can be calculated by taking ratio of activity in the two channels
11
Q
What is the primordial colour vision system?
A
- Most mammals are dichromatic - few s cones and lots of m cones = blue and yellow system
- Compares outputs: phylogenetically old
- Purely chromatic challenge with little spatial resolution
12
Q
What is the second subsystem?
A
- About 10 mill years ago where L cone is split into red/green system
- Only old world primates has the trichromatic
- Co-evolved in certain fruits so we could forage them
13
Q
How do we distinguish wavelengths? (study)
A
- Task is to compare 3 patches of light, two are identical and you must spot the different one
- Measure smallest difference of wavelength (delta lambda)
- Very characteristic patterns of function: some wavelengths of light you can really tell difference, but in others, we cannot
- High ratio differences are red/green and blue/yellow
14
Q
What are the types of colour blindness?
A
- Monochromats: only have 1 cone or just rods - very rare
- Dichromats
- Anomalous trichromacies
15
Q
What are the types of Dichromats?
A
- Protonopes - those who lost the first receptor (red cones) = more likely in males because found on x chromosome and men have only one X
- Deutranopes - those who do not have green cone - lack middle wavelength
- Tritanopes: Lack short wavelength cone = very rare
