THE BASIC NORMAL HUMAN COLOR VISION SYSTEM The visible Spectrum The visible spectrum is the portion of the electromagnetic spectrum with wavelengths between 380 nm and 760 nm. These frequencies are sensed as the following colors (wavelengths are the centers of the colors): 400 nm violet

400 nm violet 440 nm blue

440 nm blue 490 nm cyan

490 nm cyan 530 nm green

530 nm green 575 nm yellow

575 nm yellow 590 nm orange

590 nm orange 650 nm red Four kinds of sensors: Use the chart of light sensitivity curves at right. Rods Rods are primarily used at night, because they are much more sensitive than the cones. But they also provide motion and edge detection in brighter light. They are sensitive to a range of wavelengths between 380 nm and 650 nm, peaking at 530 nm. This covers the colors violet, blue, cyan, green, yellow, and orange. But rods are encoded as white, not as any specific color.

Blue Sensitive Cones The blue sensitive cones are sensitive to a range of wavelengths between 380 nm and 550 nm, peaking at 450 nm. This includes violet, blue, and cyan light.

Green Sensitive Cones The green sensitive cones are sensitive to a range of wavelengths between 430 nm and 670 nm, peaking at 550 nm. This includes cyan, green, yellow, and orange light.

Red Sensitive Cones The red sensitive cones are sensitive to two ranges of wavelengths. The major range is between 500 nm and 760 nm, peaking at 600 nm. This includes green, yellow, orange, and red light. The minor range is between 380 nm and 450 nm, peaking at 430 nm. This includes violet and some blue. The minor range is what makes the hues appear to form a circle instead of a straight line. Seeing other colors: Violet activates the blue cone, and partially activates the red cone.

Violet activates the blue cone, and partially activates the red cone. Blue activates the blue cone.

Blue activates the blue cone. Cyan activates the blue cone and the green cone.

Cyan activates the blue cone and the green cone. Green activates the green cone, and slightly activates the red and blue cones.

Green activates the green cone, and slightly activates the red and blue cones. Yellow activates the green cone and the red cone.

Yellow activates the green cone and the red cone. Orange activates the red cone, and partially activates the green cone.

Orange activates the red cone, and partially activates the green cone. Red activates the red cone.

Red activates the red cone. Magenta activates the red cone and the blue cone.

Magenta activates the red cone and the blue cone. White activates the red cone, the green cone, and the blue cone. Colors not listed here are seen due to varying strengths of light activating the red, green, and blue cones. Note that some people with protanomaly, deuteranomaly, or tritanomaly may see the correct colors, rather than the distorted colors they normally see, when viewing the above colors on a 3-color monitor. After the cones have received the colors, the color information is encoded in the bipolar and ganglion cells in the retina before it is passed on to the brain. Three different encodings are used: The primary encoding is luminance (brightness). It is the sum of the signals coming from the red cones, the green cones, the blue cones, and the rods. These provide the fine detail of the image in black and white. A second form of encoding is used to separate blue and yellow (yellow being the sum of red and green). The signal changes one way if blue is stronger than yellow, and changes in the opposite way if yellow is stronger than blue. The third form of encoding is used to separate red and green. The signal changes one way if green is stronger than red, and changes the other way if red is stronger than green. The second and third kind of encoding do not have quite the fine resolution the luminance encoding has. Black and white vision has finer detail than color vision. In the fovea, where central vision occurs, each luminance ganglion cell receives signal from only one cone cell of each color. There are no rod cells in the fovea, so it is night blind. It is interesting that the light has to pass through the ganglion and bipolar cells to get to the rods and cones. The retina seems to be made backward. But this might protect the light sensitive cells from damage. Note that the genes for the cone cells have two segments. One segment encodes a protein making an alternating grid with the proper spacing to be affected by certain colors of light. The rods and the different kinds of cone cells have different grid spacings, so they are sensitive to different colors. A rough diagram of the grid is shown at right. Notice the equally spaced rows of alpha-helix configured amino acids in the molecule. The spacings line up with the wavelength of the light of the color the molecule is sensitive too. Light in the right color band effectively rattles the entire molecule.

The other segment of the gene tells the cone cell which bipolar cell nerve endings to connect to, so the color signals are properly encoded to be sent to the brain. For more on this, see Human Color Vision.

KINDS AND EFFECTS OF DEFECTIVE COLOR VISION These are the major types of color vision defects: Protanopia - The loss of the red-sensitive cells A person with protanopia sees in tints and shades of the colors yellow and blue. Red objects look very dark.

Deuteranopia - The loss of the green-sensitive cells A person with deuteranopia sees in tints and shades of the colors yellow and blue. Green objects are slightly darker than normal. This is also called deutanopia.

Tritanopia - The loss of the blue-sensitive cells A person with tritanopia sees in tints and shades of the colors red and green. Blue objects look dark.

Tetartanopia - Undocumented loss of sensitivity to yellow (see inset)

Protanomaly - The red sensitive cells are sensitive to leaf green (yellow green) instead of red A person with protanomaly sees full color, but some oranges, yellows, greens, and browns are seen as the wrong color.

Deuteranomaly - The green sensitive cells are sensitive to yellow instead A person with deuteranomaly sees full color, but some oranges, yellows, greens, and browns are seen as the wrong color.

Tritanomaly - The blue sensitive cells are sensitive to cyan instead A person with tritanomaly sees full color, but some magentas, violets, blues, cyans, and greens are seen as the wrong color.

Red-Green Indistinction - No red-green differentiation but no sensitivity changes A person with red-green indistinction sees in tints and shades of yellow and blue. All objects are the correct brightness (no change in spectral sensitivity). Causes include missing bipolar cells differentiating red and green, or red and green pigments mixed in the same kind of cone cell.

Red-Green anomaly - Both the red sensitive cells and the green sensitive cells respond to the wrong colors. A person with red-green anomaly sees color, but some reds, oranges, yellows, greens, and browns are seen as the wrong color. Red-green anomaly is protanomaly and deuteranomaly in the same person.

Cone Monochromatism - Only the blue sensitive cells and the rods work A person with cone monochromatism sees the world in black and white. Green and yellow appear dark, and red appears black.

Rod monochromatism - Only the rods work A person with rod monochromatism sees the world in black and white. Reds appear black. The person can not see well in bright light. DEFECTIVE COLOR VISION Outer ring:

Normal color vision Second ring:

Protanopia Third ring:

Deuteranopia Inner ring:

Tritanopia More Definitions Protan - Refers to any defect in the red cone, including protanopia and protanomaly

Deutan - Refers to any defect in the green cone, including deuteranopia and deuteranomaly.

Tritan - Refers to any defect in the blue cone, including tritanopia and tritanomaly. Tetartanopia is very rare, if it exists at all. It might be a failure of the bipolar cells for blue-yellow differentiation. Or it might have been an attempt to provide a missing disease that the Hering Opponent Color theory predicted.

The genes for rod and cone cells have two segments. One segment encodes the color sensor protein, the other segment tells the cell which bipolar cell nerve endings to connect to for encoding lightness and color. There are several factors that interact to produce the kinds of defective color vision observed: The blue cone cell gene (chromosome 7) and rod cell gene (chromosome 3) are in widely separated places on different chromosomes.

The red and green cone genes are next to each other on the same chromosome, making copying errors more likely for those genes.

The red and green genes are on the X chromosome. This makes a difference between men and women for the kinds of observed defects in color vision.

The bipolar cells cause defects in the sensors to be encoded as colors in certain ways.

The defects could also be in the bipolar cells or ganglion cells (but this is rare if it happens at all). How color vision defects are interrelated: Defective color responses for red and for green vision are related, because the genes are on the same chromosome.

Defective color responses for red and for green vision are also sex-linked, because they are on the X chromosome.

There is a site on another chromosome that can remove all cone vision if it is damaged.

Other than those, color vision defects are independent of each other.

Defects that affect only red-green vision are independent of defects that affect only blue vision. There are several ways a gene can be altered to produce defective color vision: The gene can be damaged so it stops working. The gene for the color reception grid can be damaged, so the grid responds to the wrong color. The color reception grid is copied from the wrong gene (usually this affects red and green). Only part of the color reception grid is copied from the wrong gene. The wrong bipolar cell nerve connection is encoded in the gene. Multiple color reception grid types are placed into the same cones. A type of bipolar cell is missing or is connected wrong (rare if extant at all). A type of ganglion cell is missing or connected wrong (rare if extant at all). Male A gene is represented here in the following way: ---CONE The letters CONE indicate the color reception grid, the --- indicates the bipolar cell nerve endings to use. The observed red-green color variants in men (one X chromosome) include the following: Case Gene Structure Seen as

Red

(peak) Seen as

Green

(peak) Type of Defect Observed Effects 0 ---CONE ---CONE (peak) (peak) Normal Color vision Trichromatic vision 1 ---CONE ---CONE

(peak) Missing red cone gene Protanopia - Red blind (also called red-green blindness) 2 --- CONE ---CONE (peak) (peak) Green pigments with red and green encoding Protanopia (variant) - Red blind (also called red-green blindness) 3 --- CONE ---CONE (peak)

Green cone with red encoding Protanopia (variant) - Red blind (also called red-green blindness) 4 ---CO NE ---CONE (peak) (peak) Red cone is a yellow cone instead Protanomaly - Red weak 5A ---CO NE ---CONE (peak)

Yellow (red + green) cone with red encoding Red-Green Indistinction - Red-Green blind 5B ---CONE --- CONE (peak) (peak) Red and green pigments with red encoding Red-Green Indistinction - Red-Green blind 6A ---CONE ---CO NE

(peak) Yellow (red + green) cone with green encoding Red-Green Indistinction - Red-Green blind 6B --- CONE ---CONE

(peak) Red and green pigments with green encoding Red-Green Indistinction - Red-Green blind 7 ---CONE ---CO NE (peak) (peak) Green cone is a yellow cone instead Deuteranomaly - Green weak 8 ---CONE --- CONE

(peak) Red cone with green encoding Deuteranopia (variant) - Green blind (also called red-green blindness) 9 ---CONE --- CONE (peak) (peak) Red pigments with red and green encoding Deuteranopia (variant) - Green blind (also called red-green blindness) 10 ---CONE ---CONE (peak)

Missing green cone gene Deuteranopia - Green blind (also called red-green blindness) Since cases 5A and 5B are visually identical and have identical hereditary results, they can be counted as case 5 for the rest of this page. Since cases 6A and 6B are visually identical and have identical hereditary results, they can be counted as case 6. Cases 1, 2, and 3 produce the same visual result, but have different hereditary results. They must be counted as separate cases. Cases 8, 9, and 10 produce the same visual result, but have different hereditary results. They must be counted as separate cases. Note that the color "yellow" in cases 4, 5A, 6A, and 7 is generic, and can refer to any color between leaf green and orange. The precise color depends on how much of each gene is retained in the hybrid. Female The case for a female subject is more involved, because there are two X chromosomes. The possible cases become the cross product of the two X chromosomes. But note that almost all cases of defective color vision in females are in the top row or the left column. The others are rare. This is a table of possible defective color vision in females. The first number is the visual case. The number after the C means the female is a carrier of the numbered genes. The last line shows possibilities for males: X Mother

Father ---CONE 0

---CONE ---CONE 1

---CONE --- CONE 2

---CONE --- CONE 3

---CONE ---CO NE 4

---CONE ---CO NE 5

---CONE ---CONE 6

---CO NE ---CONE 7

---CO NE ---CONE 8

--- CONE ---CONE 9

--- CONE ---CONE 10

---CONE ---CONE 0

---CONE 0 Normal

(p) (p) 0 C:1

(p) (p) 4 C:2

(p) (p) 4 C:3

(p) (p) 11 C:4

(p) (p) 11 C:5

(p) (p) 12 C:6

(p) (p) 12 C:7

(p) (p) 7 C:8

(p) (p) 7 C:9

(p) (p) 0 C:10

(p) (p) ---CONE 1

---CONE 0 C:1

(p) (p) 1 C:1

(p) (p) 2 C:1,2

(p) (p) 2 C:1,3

(p) (p) 4 C:1,4

(p) (p) 4 C:1,5

(p) (p) 13 C:1,6

(p) (p) 12 C:1,7

(p) (p) 6 C:1,8

(p) (p) 7 C:1.9

(p) (p) 0 C:1,10

(p) (p) --- CONE 2

---CONE 4 C:2

(p) (p) 2 C:1,2

(p) (p) 2 C:2

(p) (p) 2 C:2,3

(p) (p) 15 C:2,4

(p) (p) 15 C:2,5

(p) (p) 15* C:2,6

(p) (p) 17 C:2,7

(p) (p) 4* C:2,8

(p) (p) 20 C:2,9

(p) (p) 4 C:2,10

(p) (p) --- CONE 3

---CONE 4 C:3

(p) (p) 2 C:1,3

(p) (p) 2 C:2,3

(p) (p) 3 C:3

(p) (p) 15 C:3,4

(p) (p) 13* C:3,5

(p) (p) 4* C:3,6

(p) (p) 20 C:3,7

(p) (p) 0* C:3,8

(p) (p) 7* C:3,9

(p) (p) 5 C:3,10

(p) (p) ---CO NE 4

---CONE 11 C:4

(p) (p) 4 C:1,4

(p) (p) 15 C:2,4

(p) (p) 15 C:3,4

(p) (p) 4 C:4

(p) (p) 4 C:4,5

(p) (p) 17 C:4,6

(p) (p) 19 C:4,7

(p) (p) 20 C:4,8

(p) (p) 18 C:4,9

(p) (p) 11 C:4,10

(p) (p) ---CO NE 5

---CONE 11 C:5

(p) (p) 4 C:1,5

(p) (p) 15 C:2,5

(p) (p) 13* C:3,5

(p) (p) 4 C:4,5

(p) (p) 5 C:5

(p) (p) 20 C:5,6

(p) (p) 18 C:5,7

(p) (p) 7* C:5,8

(p) (p) 16* C:5,9

(p) (p) 14 C:5,10

(p) (p) ---CONE 6

---CO NE 12 C:6

(p) (p) 13 C:1,6

(p) (p) 15* C:2,6

(p) (p) 4* C:3,6

(p) (p) 17 C:4,6

(p) (p) 20 C:5,6

(p) (p) 6 C:6

(p) (p) 7 C:6,7

(p) (p) 14* C:6,8

(p) (p) 16 C:6,9

(p) (p) 7 C:6,10

(p) (p) ---CONE 7

---CO NE 12 C:7

(p) (p) 12 C:1,7

(p) (p) 17 C:2,7

(p) (p) 20 C:3,7

(p) (p) 19 C:4,7

(p) (p) 18 C:5,7

(p) (p) 7 C:6,7

(p) (p) 7 C:7

(p) (p) 16 C:7,8

(p) (p) 16 C:7,9

(p) (p) 7 C:7,10

(p) (p) ---CONE 8

--- CONE 7 C:8

(p) (p) 6 C:1,8

(p) (p) 4* C:2,8

(p) (p) 0* C:3,8

(p) (p) 20 C:4,8

(p) (p) 17* C:5,8

(p) (p) 14* C:6,8

(p) (p) 16 C:7,8

(p) (p) 8 C:8

(p) (p) 9 C:8,9

(p) (p) 9 C:8,10

(p) (p) ---CONE 9

--- CONE 7 C:9

(p) (p) 7 C:1,9

(p) (p) 20 C:2,9

(p) (p) 7* C:3,9

(p) (p) 18 C:4,9

(p) (p) 16* C:5,9

(p) (p) 16 C:6,9

(p) (p) 16 C:7,9

(p) (p) 9 C:8,9

(p) (p) 9 C:9

(p) (p) 9 C:9,10

(p) (p) ---CONE 10

---CONE 0 C:10

(p) (p) 0 C:1,10

(p) (p) 4 C:2,10

(p) (p) 5 C:3,10

(p) (p) 11 C:4,10

(p) (p) 14 C:5,10

(p) (p) 7 C:6,10

(p) (p) 7 C:7,10

(p) (p) 9 C:8,10

(p) (p) 9 C:9,10

(p) (p) 10 C:10

(p) (p)

Male 0 Normal

(p) (p) 1

(p) (p) 2

(p) (p) 3

(p) (p) 4

(p) (p) 5

(p) (p) 6

(p) (p) 7

(p) (p) 8

(p) (p) 9

(p) (p) 10

(p) (p) * = The red cone and green cone functions are traded, with the red cone detecting a shorter wavelength than the green cone does. The extra visual anomalies found only in females are listed below. Other gene combinations producing the same color sensations are possible: Case Gene Structure Seen as

Red

(peak) Seen as

Green

(peak) Type of Defect Observed Effects 0* ---CONE --- CONE

--- CONE ---CONE (peak) (peak) Normal color vision with red and green traded Trichromatic vision and double dichromat carrier

Maybe not aware of traded red and green functions. 11 ---CONE ---CONE

---CO NE ---CONE (peak) (peak) Red cone shifted to orange Protanomaly (variant) 12 ---CONE ---CONE

---CONE ---CO NE (peak) (peak) Green cone shifted to leaf Deuteranomaly (variant) 13 ---CONE ---CONE

---CONE ---CO NE (peak) (peak) Green cone shifted to leaf, no red cone Deuteranomalous Protanopia - Red blind, green defective 14 ---CONE ---CONE

---CO NE ---CONE (peak) (peak) Red cone shifted to orange, no green cone. Protanomalous Deuteranopia - Green blind, red defective 15 --- CONE ---CONE

---CO NE ---CONE (peak) (peak) Red cone shifted to leaf Protanomaly (variant) 16 ---CONE --- CONE

---CONE ---CO NE (peak) (peak) Green cone shifted to orange Deuteranomaly (variant) 17 ---CONE ---CO NE

--- CONE ---CONE (peak) (peak) Red cone shifted to yellow, green cone shifted to leaf Red-Green Anomaly (variant) 18 ---CONE --- CONE

---CO NE ---CONE (peak) (peak) Red cone shifted to orange, green cone shifted to yellow Red-Green Anomaly (variant) 19 ---CONE ---CO NE

---CO NE ---CONE (peak) (peak) Red cone shifted to orange, green cone shifted to leaf Red-Green Anomaly (variant) 20 ---CONE --- CONE

--- CONE ---CONE (peak) (peak) Red cone and green cone both shifted to yellow Red-Green Indistinction What about tetrachromacy in females? Some of the above cases of protanomaly and deuteranomaly could possibly produce eyes with 4 different color sensitive pigments. But what kind of vision this produces depends on how the pigments are distributed and what kind of nerve connections to the brain are created: Case 1: One kind of cone has two pigments. Three neural pathways. In this case, the response curve of the cone is altered, making the vision system ultrasensitive to color changes in certain parts of the spectrum that normal people can't distinguish, but insensitive to color differences other people notice.

Case 2: Four kinds of cones, but two are identically connected to the nervous system. Three neural pathways. In this case, the response curve of the combination of cones is altered, making the vision system ultrasensitive to color changes in certain parts of the spectrum that normal people can't distinguish, but insensitive to color differences other people notice.

Case 3: Four kinds of cones. Four neural pathways, with an extra differencing network for the extra colors. In this case, there is a genuine increase in the number of colors visible to the person. This system can notice changes in the spectral emission curve of the light source, including spectral gaps not noticed by other people. It makes the vision system ultrasensitive to color changes in certain parts of the spectrum that normal people can't distinguish, but not reducing sensitivity to color differences other people notice. Note that adding a human gene for a green cone to mice (dichromatic, blue and yellow) did not give them trichromatic vision. It made two kinds of cone cells, but did not make a differencing network to tell the difference between green and red.