colour vision Flashcards
Wavelength
Varies smoothly and evenly but our perception of colour doesn’t
Colour mixing
Most light we see from the sun is white
When we mix types of light together we see different colours
Colour addition
Any single wavelength can be perfectly matched by a mixture of three other wavelengths
Trichromacy theory
Rod receptors
Rods only useful when not a light of around
Help us in low light conditions like climbing up the stairs when the light is off
Red cone
Long wavelength cone
564nm
Get a lot of them
Green cone
Medium wavelength cone
534nm
Get a lot of them
Blue cone
Short wavelength cone
420nm
Don’t get many of them
Colour perception
Each type of cone responds to a range of wavelengths but has peak sensitivity at their set nm
Colour matching experiements
Trichromacy theory supported because we can make any colour by adjusting intensity of three colours of light
RGB - like stardew
Principle of univariance
If we only operate with rods, it can’t detect changes in intensity and wavelength
No way of telling if the change is in intensity or wavelength
Human suffer the changes in univariance at night
Brain detects changes in brightness, no changes in colour
Two receptor system
Each stimulus activates both receptors in different ratios
Ratio doesn’t change changes in intensity
Colour can be calculated by looking at the ratio of activity in the two channels
How to calculate colour in two receptor system
Take output of each cone to look at colour and total amount for brightness
Two types of cones are necessary to perceive wavelengths, with only one cone it only detects variations in brightness
If one medium wavelength cone is used it will be stimulated the same by a high intensity red light or a low intensity blue light
Primordial system
Most mammals are dichromatic with few short wavelength cones and lots of medium cones
Blue/yellow system
Little spatial resolution
Second subsystem
Long wavelength cones split into two to make a red/green system
Old world primates
Evolved with certain fruits so we could forage them
Monochromats
Only have one cone type or just rods
Dichromats - Protanopes
Lack long wavelength cone (red)
Dichromats - Deutranopes
Lack middle wavelength cone (green)
Dichromats - Tritanopes
Lack short wavelength cone (blue)
Anomalous trichromats - Protanomaly
Abnormal long wavelength cone
Anomalous trichromats - Deuteranomaly
Abnormal medium wavelength cone
Opponent processes
Two subsystems of colour vision
How opponent processes work
Process of excitatory and inhibitory responses, with the two components of each mechanism opposing each other
Red creates positive response in a cell, green creates inhibitory response
When this cell is activated it tells the brain that you are seeing red
What does antagonistic interaction help with
Help visual system detect colour contrasts and edges more effectively
Comparison of short with long/medium (blue/yellow)
Not spatially antagonistic
Does not have the excitatory and inhibitory responses of red/green
Old shared with other mammals
Own ganglion cells to koniocellular layers of LGN and then layers 2-3 of V1
Comparison of medium with long (red/green)
Spatially antagonistic
New to old world primates
To parvocellular layers of LGN
Layer 4ca of V1
Piggybacked on the existing colour system
Colour constancy
Our ability to work out colours despite large changes in wavelength of the lighting
Colour of the dress changes depending on what our brain thinks the illumination is
Colour aftereffect and opponent processes
When staring at an image for too long, the relevant cells in the opponent cells (red and white) will be fatigued and start sending weaker signals to save energy
When you shift our focus the cells no longer have the stimuli telling them to fire, so the white and red receptor cells will de-activate, leaving our black and green cells to activate in response
If you stare at the inverted Welsh flag for too long, then move away, it will look normal because of the opposing cells firing
