Textbook Notes (368,432)
Canada (161,877)
Psychology (1,468)
PSYCH 1XX3 (384)
Joe Kim (3)

Colour Perception.docx

8 Pages
Unlock Document

Joe Kim

Colour Perception (Week 6) Introduction to Colour Perception • The reason we can see different colours is because the objects and surfaces we look at reflect certain wavelengths of the visible spectrum. • These reflected wavelengths trigger specific patterns of responses in the brain that give rise to our subjective experience of colour • The subjective experiences relates to how the different wavelengths of light affect certain cones in our retina • The composition of wavelength reflected by an object is determined by its reflectance and the wavelength composition if the illuminating light • Colour constancy is the ability of colour vision to correct the variation in overall illumination(brightness) so that an object’s colour appears the same all the time Evolution of Colour Perception: Why and Who • A bull does not react to the red cap, the bulls response is more or likely to the motion of the cap • Colour vision in mammals is limited to primates, including humans (cats, dogs, and fish see in shades of grey). • Primates colour vision is well suited to distinguish red and yellow against a green background, helping us to find fruit in bushes. The ability to see colour gives us an advantage to detect predators and prey against a background The Functions of Colour Vision in Different Species • Many birds, fish, reptiles and insects are able to see colour that we don’t see, including colours at the UV end of the spectrum • The colour of a birds feather indicates to other potential mates their health Variation of Colour Vision • Humans, bees, and macaque monkeys are trichromats • Bees are sensitive to ultraviolet light • Goldfish, pigeons, and ducks have eyes containing four types of receptors • Rabbits, cats, and squirrels are dichromatic(only two types of receptors) • Any animal that is monochromatic lacks chromatic vision entirely, and must resolve object by differences in brightness and contrast Colour Mixing • Only a few receptors types are needed that can be combined in various proportions to make every conceivable colour • The three primary colours can be combined in various proportions to make every colour in the spectrum • Primary colours cannot be further reduced into other colours Subtractive Colour Mixing • Applies to the mixing of pigments, dyes, or paints and it is called ‘subtractive’ because every surface colour absorbs (or subtracts) the colours it does not reflect. Adding other pigments to the surface alters the combination wavelengths subtracted • The complementary colour of red was green; for yellow it was purple; and blue it was orange • If a primary colour is mixed with its complementary colour you get brown • Summary: involves a combination of pigments reflecting the sum of wavelengths that are not absorbed Additive Colour Mixing • The mixing of coloured lights • Coloured lights add their dominant wavelengths to the mixture as opposed to subtracting wavelengths out • This is how our visual system processes colour, by adding the effects of different wavelengths together in the nervous system • The primary colours with additive colour mixing are red, green and blue , because these three colours can be added together in various proportions to make all the colours we see • The complementary colour of blue is yellow; for the red is a bluish-green(teal); and for green the complementary colour is a redish-purple • When every a primary colour is mixed with its complementary colour you get grey or white • The mixing of blue and yellow produces grey Trichromatic Theory (Young-Helmholtz theory)(Retina) • Is based on the proposal that the retina contains three different kinds of receptors, that are each maximally sensitive to different wavelengths of light • This theory is based off the idea that it is possible to match all of the colours of visible spectrum by the appropriate mixing of 3 primary colours • Thus, meaning only three different types of receptors are needed to discriminate all the colours of the visible spectrum • It is now known that indeed the retina is equipped with three types of cones which contain spectrally selective photopigments that are maximally responsive to wavelengths of light that correspond to the primary colours red, green and blue • A receptor will respond to other wavelengths to , just not as much as it would to its peak wavelength • White is what you see when all three receptors are stimulated • Downfalls to the theory: 1. Yellow seemed to be a primary colour and not a mixture of red and green 2. Couldn’t explain the law of complementarity , that certain wavelengths produce the experience of white 3. Couldn’t answer the question of why we see yellow afterimage when staring at a blue stimulus Opponent-Process Theory of Colour Vision(Ganglion Cells) • Argues that there are three classes of receptors, but each of these receptors is made up of a pair of opponent processes • Each receptor is capable of being in one of two opponent states at a time • The ability to see blues and yellows is mediated by a blue-yellow opponent receptors • The ability to see greens and reds is mediated buy a green-red opponent receptor • The third type of opponent receptor distinguishes between bright and dim light ; these brightness detectors are excited by lights of any wavelengths • Used to explain how a mixture of wavelengths from complementary colours(like blue and yellow) appear white, why the afterimaging of a stimulus is the complementary colour Both Theories Needed to Explain Colour Perception • Hurvich and Jameson elaborated the theories and proposed that: 1. There are three component receptors or cones in the retina that are maximally responsive to light of a certain wavelength (trichromatic theory). The three cones are maximally responsive to red, green, and blue. The responsive of these receptors affect what is happening in the brain, where things are organized as the opponent-process theory would predict 2. The opponent pairs are red-green, blue-yellow, and light-dark 3. The combination of the two theories says that the output of the cones is input for the next layer of colour processing in the retina, which is organized in an opponent fashion. Colour coding continues in this opponent arrangement into the brain’s visual processing system • Example: A red light would stimulate a red cone in the retina, which would then excite the red-green ganglion cells that are organized in an opponent fashion, and this excitation of the red-green ganglion cell would signal the brain that the stimulus is red. A green light (blue light), would stimulate a green cone (blue cone), which would inhibit the red-green (yellow-blue) ganglion cell. The inhibition of the red-green cell would signal that the stimulus is green. • Example: Yellow is a mixture of red a
More Less

Related notes for PSYCH 1XX3

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.