Three Main Theories of Color Vision
There are a number of theories related to color vision and color blindness, but the three very
important and famous theories are;
1. Parallel processing theory of vision
2. Trichromatic theory of color vision
3. Opponent- process theory of color vision
I. Parallel Processing Theory of Vision
• The brain’s distinctive and natural way of processing information in which various aspects of information are processed simultaneously__ includes many brain functions such as vision; contrasts with the serial/ step- by- step processing of most computers and of conscious problem solving
• Unlike most computers, which work/ processes information instantly through step- by- step serial processing, humansdo parallel processing___ means do several things at one time
• Our brain is capable of dividing visual information into various dimensions/ categories
such as color, depth, movement etc and works on each aspect/ part simultaneously
• Visual information is processed in the following manner. i.e.
o One looks at someone/ something
o Information is sent to the brain
o The component features are reassembled and,
o In, still not a clearly and exactly known way, the scene is combined/ composed into the consciously perceived meaningful image
Parallel Processing Theory of Vision
Trichromatic Theory
•Initially by Sir Thomas Young, and later developed as Young-Helmholtz Trichromatic Theory of Color
vision
•The retina contains three types of cones. Each type responds to specificrange of wave length
Hering’s Opponent- Process Theory
•The receptor cells are linked in pairs and they work in opposition to each other
•There is a black- white pairing, a blue- yellow pairing, and a red- green pairing
•If an object reflects light containing more green than red, it will stimulates the firing of the cells sensitive
to green, at the same time inhibiting the firing of red- sensitive cells; the object will thus appear green
•This theory explains the phenomenon of after- image very well
Color Vision Deficiencies: Congenital And Acquired
• Color vision deficiencies are classified into congenital and acquired
• Congenital deficiencies are due to the inborn abnormality of cone photoreceptor cells
• Acquired deficiencies results any time after birth___ occur due to the disorders that affect the eye or/ and the brain
• In both of these deficiencies, people experience colors differently from those with normal trichromatic color vision
I.Dichromacy
II.Anomalous trichromacy
III.Rod monochromacy
I. Dichromacy
• Individuals with this deficiency are able to match all the colors using two primaries rather
than three
• Dichromatic miss one of the three cone types
There are the following three main types of dichromacy, which are named on the basis of cone photo
pigment that is missing. They are;
1. Protanopia
2. Deuteranopia
3. Tritanopia
• Both protanopia and deuteranopia are sex-linked i.e. inherited recessively from a gene located on the X
chromosome
• If this deficiency is inherited, males (XY) will manifest it because they have only one X
chromosome__females (XX) have two X chromosomes, so they will only be color deficient if the
deficiency is carried on to both X chromosomes. They can pass this condition to their male offspring
without being color deficient themselves ProtanopiaRed photo pigment is absent and is replaced by the
medium green photo pigment due to this; people with this deficiency confuse red and green color
• See shorter wavelengths such as blue
Deuteranopia Also confuse red and green
It is sex- linked deficiencyand effect about 1% of males and .01% of females
Tritanopia
Basis of this deficiency is not yet clear__ may occur due to the absence of short wavelengths such as blue
People with this deficiency are insensitive to blues and yellows and see the world in red and green
A very rare condition and occur only in.002% of males and .001% of females.
Anomalous trichromacy
• People with this deficiency mix the primaries in different proportions
• Like normal trichromats, these peoplealso need three wave lengths___ but due to spectral sensitivities,
they often mingled them up
Rod monochromacy
• Extremely rare hereditary condition which occurs due to the absence of cones in the eye
• As vision is dependent on the rods photoreceptors, the acuity is very weak because of the absence of
cones
• Absence of cones are also responsible for poor fixation, erratic eye movements, visual fields defects and
serious refractive error
Color Blindness
•Inability to see specific colors
•25 of men and 2 out of 10,000 women are color blind
•Red- green color blindness; inability to distinguish red from green
•Yellow-blue; the person can not differentiate between yellow and blue
•Monochromatic color blindness; inability to perceive any color at all
•The Trichromatic theory explains this phenomenon very well
important and famous theories are;
1. Parallel processing theory of vision
2. Trichromatic theory of color vision
3. Opponent- process theory of color vision
I. Parallel Processing Theory of Vision
• The brain’s distinctive and natural way of processing information in which various aspects of information are processed simultaneously__ includes many brain functions such as vision; contrasts with the serial/ step- by- step processing of most computers and of conscious problem solving
• Unlike most computers, which work/ processes information instantly through step- by- step serial processing, humansdo parallel processing___ means do several things at one time
• Our brain is capable of dividing visual information into various dimensions/ categories
such as color, depth, movement etc and works on each aspect/ part simultaneously
• Visual information is processed in the following manner. i.e.
o One looks at someone/ something
o Information is sent to the brain
o The component features are reassembled and,
o In, still not a clearly and exactly known way, the scene is combined/ composed into the consciously perceived meaningful image
Parallel Processing Theory of Vision
Trichromatic Theory
•Initially by Sir Thomas Young, and later developed as Young-Helmholtz Trichromatic Theory of Color
vision
•The retina contains three types of cones. Each type responds to specificrange of wave length
Hering’s Opponent- Process Theory
•The receptor cells are linked in pairs and they work in opposition to each other
•There is a black- white pairing, a blue- yellow pairing, and a red- green pairing
•If an object reflects light containing more green than red, it will stimulates the firing of the cells sensitive
to green, at the same time inhibiting the firing of red- sensitive cells; the object will thus appear green
•This theory explains the phenomenon of after- image very well
Color Vision Deficiencies: Congenital And Acquired
• Color vision deficiencies are classified into congenital and acquired
• Congenital deficiencies are due to the inborn abnormality of cone photoreceptor cells
• Acquired deficiencies results any time after birth___ occur due to the disorders that affect the eye or/ and the brain
• In both of these deficiencies, people experience colors differently from those with normal trichromatic color vision
I.Dichromacy
II.Anomalous trichromacy
III.Rod monochromacy
I. Dichromacy
• Individuals with this deficiency are able to match all the colors using two primaries rather
than three
• Dichromatic miss one of the three cone types
There are the following three main types of dichromacy, which are named on the basis of cone photo
pigment that is missing. They are;
1. Protanopia
2. Deuteranopia
3. Tritanopia
• Both protanopia and deuteranopia are sex-linked i.e. inherited recessively from a gene located on the X
chromosome
• If this deficiency is inherited, males (XY) will manifest it because they have only one X
chromosome__females (XX) have two X chromosomes, so they will only be color deficient if the
deficiency is carried on to both X chromosomes. They can pass this condition to their male offspring
without being color deficient themselves ProtanopiaRed photo pigment is absent and is replaced by the
medium green photo pigment due to this; people with this deficiency confuse red and green color
• See shorter wavelengths such as blue
Deuteranopia Also confuse red and green
It is sex- linked deficiencyand effect about 1% of males and .01% of females
Tritanopia
Basis of this deficiency is not yet clear__ may occur due to the absence of short wavelengths such as blue
People with this deficiency are insensitive to blues and yellows and see the world in red and green
A very rare condition and occur only in.002% of males and .001% of females.
Anomalous trichromacy
• People with this deficiency mix the primaries in different proportions
• Like normal trichromats, these peoplealso need three wave lengths___ but due to spectral sensitivities,
they often mingled them up
Rod monochromacy
• Extremely rare hereditary condition which occurs due to the absence of cones in the eye
• As vision is dependent on the rods photoreceptors, the acuity is very weak because of the absence of
cones
• Absence of cones are also responsible for poor fixation, erratic eye movements, visual fields defects and
serious refractive error
Color Blindness
•Inability to see specific colors
•25 of men and 2 out of 10,000 women are color blind
•Red- green color blindness; inability to distinguish red from green
•Yellow-blue; the person can not differentiate between yellow and blue
•Monochromatic color blindness; inability to perceive any color at all
•The Trichromatic theory explains this phenomenon very well
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