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Lecture 5

PSYB51H3 Lecture Notes - Lecture 5: Monochromacy, Trichromacy, Motion Aftereffect

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Matthias Niemeier

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Lecture 5 Psyb51
Newtons discovery
If you send white light through an aperture of a glass prism the light will fan out because of
Why does this happen??
o Different wave lengths bend differently
Monochromatic colours: single wavelength/cannot be broken down into anymore wavelengths
Red and blue are single wavelengths and cannot be broken down like white light
White is a mix of different wavelengths
Three cones in out eyes that let us see millions of colours
Rubix Cube
Two coloured squares on the rubix cube may appear as two different colours due to context but
when you remove context the colours become the same
Context changes the way that we see colours
Possible to see different wavelengths as the same colour
Colour perception is ambiguous
Colour help with the detection of objects
The perception of colour
Clown image
o Image is made up of three different wave lengths (blue, green and red)
Univariance: a single cone cannot give us the information on any colours out in the real world. An
infinite set of different wavelength intensity combinations can elicit the same response from a single
type of photoreceptor.
E. Gree rods do’t see gree i di light
One cone cannot provide us with colour
If we only had green cones we would only see black and white
Different wave lengths see things at different intensities
One type of photoreceptor cannot discriminate between colours based on wavelengths
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Y Axis= the output of the receptor
Each wavelength has the same amount of energy but causes cones differently
The input is always the same in energy. But the output is always different
Each photoreceptor responds differently to wave lengths
We can adjust the energy of the different wavelengths of the shined onto a photoreceptor and
arrive at the same output.
We perceive dim light as grey (scotopic/night vision) because cones do not work in dim light
only rods
All include the photopigment rhodopsin
Rods peak for green light
All rods have the same sensitivity to wavelengths and this makes it impossible to discriminate
light of different wavelength
Young-Helmholtz and Maxwell Theory: colour vision is based on 3 photoreceptors sensitive to ranges of
If you shined a monochromatic (single wavelength) light that appears blueish onto
something, it looks the same as if you were to mix 3 colours onto something
You can recreate any monochromatic night by using red, blue, and green
S cones= short wavelengths at 420nm (blue cones)
M cones= medium wavelengths at 534nm (green cones)
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L ones= long wavelengths at 565 (red cones)
Center of the fovea has no s cones meaning that it is colour blind to blue
You vision is slightly more blurred for blue in dim conditions
You can fix the problem of univariance with the three cones
M cones see blue and orange at the same intensity
L cones respond more to orange light that to blue light
Cones can tell the difference between all sorts of colours
The shorter the wavelengths the less light is reflected compared to higher waves lengths
Red has longer wavelengths than blue
Colour perception occurs in a 3D space
The cones define the dimensions of the 3D spaces and explains why we can see so many colours
Trichromacy is basically how colour perception is based on three colour mechanisms
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