Lecture 7: Colour Visions Flashcards
Describe light
Something that comes down, hits objects at different frequencies (wavelengths)
What part of the electromagnetic wave can humans see?
Visible light - our brain perceives these wave lengths as colour
Despite wavelength variying smoothly…
Our perception of colour is not smooth
what type of vision do humans have
Trichromatic vision (3 photo receptor types - cones)
what is colour addition? (colour mixing)
where any single (perceived) colour of wavelength can be created by made by mixing any three colours together
what is colour subtraction?
When some wavelentghs of a light source are absorbed by the object while others are reflected
What cones are in trichromatic vision?
Short cones (blue), medium (green) and long (red).
What would happen if we just had one cone?
Principle of uni variance - any one cell or cone can only respond in one way (if we perceive what three cones would see as two diff colours at the same intensity with only one cone, we will just see a single colour
Two receptor systems:
Diachromatic: stimuli will activate both receptors but in different ratios leading to the detection of the colours
Evolution of 3 cone colour vision
primordial one - most mammals had 2 cones (short and medium) but the medium cone split 10 mill years ago into two - this co evolved with the colour of fruits
Colour blindness: Monochromats
only 1 cone/just rods (very rare)
Colour blindness: Dicrhomats
Only two cones, either lack long cone (protanopes), medium (deuteranopes) and short (tritanopes)
Abnormal Trichromacy
Protanomaly/deuteranomaly
Cerebral Achromatpsia
rare condition casued by bilateral damage to V4 where patient loses ability to perceive
Colour after effect
When you look at an image for an extended period of time, and it is removed, may see a colour after effect
