PS102 Chapter Notes - Chapter 5: Retinal Ganglion Cell, Trichromacy, Color Vision

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13 Jan 2017
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Seeing in Colour:
-cones enable us to see colour, which only exists in the brain
-object reflects particular wavelength, is detected by cones, and creates chemical changes that generate
neural signal
-signal processed by brain resulting in sensation of colour
Experience of colour described along 3 dimensions:
-variety of colours we perceive is related to different combination of 3 characteristics
-using these 3 dimensions, human can detect estimated 7 million colours
1) hue
-experience of colour based on wavelength of light that visual stimulus emits or reflects
-most basic aspect of colour
-whether stimulus is perceived as red, green, orange, blue, yellow etc
2) saturation
-purity of a colour
-how bright or vivid colour appears
-if colour is desaturated, it has white or grey mixed into it
-pure red = saturated, pink = more desaturated, grey = completely desaturated
3) brightness
-how much light emanates or is reflected from visual stimulus
-light intensity
-white is the brightest colour, black the least bright
Theories of Colour Perception:
-no single theory explaining how we perceive colour
2 theories of colour vision combine to help explain a good deal:
1) Young-Helmhotlz trichromatic theory
-3 types of receptors for colour
-each type responds to different range of wavelength of light
-one receptor type responds to yellowish-red wavelengths
-typically at least 2 cone types respond to a certain wavelength of visible light in varying
increments
-combination of signals produced by cones allows brain to respond to such a multitude of
colours
2) Opponent process theory
-colour pairs work to inhibit one another in the perception of colour
-in retinal ganglion cells, thalamus, and visual cortex, colour info analyzed in terms of
antagonistic opponent colour pairs
-ex: reg-green, yellow-blue, black-white
-support: we cannot mix certain combinations of colours
-we cannot see reddish green or bluish yellow but can see greenish yellow or blueish red
-result of activity in lateral geniculate nucleus, result of activity in region of thalamus that
receives visual information
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Document Summary

Cones enable us to see colour, which only exists in the brain. Object reflects particular wavelength, is detected by cones, and creates chemical changes that generate. Signal processed by brain resulting in sensation of colour. Variety of colours we perceive is related to different combination of 3 characteristics. Using these 3 dimensions, human can detect estimated 7 million colours: hue. Experience of colour based on wavelength of light that visual stimulus emits or reflects. Whether stimulus is perceived as red, green, orange, blue, yellow etc: saturation. If colour is desaturated, it has white or grey mixed into it. Pure red = saturated, pink = more desaturated, grey = completely desaturated: brightness. How much light emanates or is reflected from visual stimulus. White is the brightest colour, black the least bright. No single theory explaining how we perceive colour. 2 theories of colour vision combine to help explain a good deal: Theories of colour perception: young-helmhotlz trichromatic theory.

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