Article - Color Vision · Web vieware active in bright light and detect different color...
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Article: Color Vision The Importance of Color Vision Eyes are, perhaps, one of nature’s greatest achievements. They observe everything from broad landscapes to precise micro-details. Color vision allows for species to interact with their environment, identify predatory threats, search and scavenge for food or shelter, and attract or recognize mates. Despite these benefits, not all species possess color vision. The ability to see color is highly dependent on adaptation and evolutionary factors. What produces color vision? As we gaze at an object, its reflected light hits the light-sensitive retina at the back of the eye. The photoreceptors in the retina, called rod and cone cells, are special types of neurons that convert light into electrical signals. The optic nerve transmits these signals to the visual cortex in the brain. Rods are extremely sensitive and active in low light. Cones are active in bright light and detect different color wavelengths. At least two cones must be present to perceive color. Some species have only one or two types of cones, while others have three or four types. What is trichromacy? Trichromacy is to possess three types of cone cells, or “normal vision” . Most humans & some other mammals are trichromatic and able to detect 1-2 million different colors. L cones detect long wavelengths of 560 nanometers, allowing for red detection & some yellow. M
Transcript of Article - Color Vision · Web vieware active in bright light and detect different color...
Article: Color VisionThe Importance of Color Vision
Eyes are, perhaps, one of nature’s greatest achievements.
They observe everything from broad landscapes to precise
micro-details. Color vision allows for species to interact with
their environment, identify predatory threats, search and
scavenge for food or shelter, and attract or recognize mates.
Despite these benefits, not all species possess color vision.
The ability to see color is highly dependent on adaptation
and evolutionary factors.
What produces color vision?
As we gaze at an object, its reflected light hits the light-sensitive retina
at the back of the eye. The photoreceptors in the retina, called rod and
cone cells, are special types of neurons that convert light into electrical
signals. The optic nerve transmits these signals to the visual cortex in
the brain. Rods are extremely sensitive and active in low light. Cones
are active in bright light and detect different color wavelengths. At least
two cones must be present to perceive color. Some species have only
one or two types of cones, while others have three or four types.
What is trichromacy?
Trichromacy is to possess three types of cone cells, or “normal
vision”. Most humans & some other mammals are trichromatic
and able to detect 1-2 million different colors. L cones detect
long wavelengths of 560 nanometers, allowing for red detection
& some yellow. M cones detect medium wavelength of 530
nanometers & allow for green detection. S cones detect small
wavelengths of 420 nanometers & allow for blue detection.
What is color blindness?
In humans, we often refer to being “colorblind” when a person
has just two types of cone cells. This is also called dichromacy.
Typically, dichromacy is inherited, as the genes for cone cells are
situated on the X-chromosome. People with color blindness may
not be aware of any differences among color that are obvious to
others. There are several kinds of color blindness. Red-green
color blindness is the most common, followed by blue-yellow color blindness. The most common type
of red-green color blindness, deuteranomaly, affects nearly 5% of the human male population. The
green cone is absent or deficient, making yellow and green appear redder, and it is difficult to tell violet
from blue. While dichromacy is considered a deficiency in humans, most mammals are dichromatic and
lack red cones. This was probably a feature of the first mammalian ancestors, which were likely small,
nocturnal, and burrowing. Dogs, for example, are
dichromatic and see shades of blue, yellow, and
grey. But where dogs lack in color vision, they
make up for in acuity. Dogs have better peripheral
vision and many more rod cells than humans,
giving them a visual acuity of 20/75 and allowing
them to see farther and with significantly more
motion sensitivity.
What is
total color blindness?
Cone monochromacy, or “total color blindness”, is the ability to
distinguish only one frequency of EM spectrum. It allows for
detection of about 100 colors, everything in shades of gray. Most
marine mammals and fish are monochromatic, as well as the
(night) owl monkey, raccoons, and some bats and rodents. In
humans, monochromacy is very rare and may be inherited or result from disease.
Can some people see more colors than me?
Studies suggest that some women may possess an
extra 4th cone that allows for detection of over 100
million colors! This is called tetrachromacy or super
color vision. Some species are thought to be
tetrachromatic as well, including some fish, mammals,
birds, reptiles, and amphibians. Goldfish contain cone
cells for red, green, blue, and ultraviolet (UV) light,
and reindeer have UV sensitivity too.
Questions1. Briefly explain the major types of vision; monochromacy, dichromacy, trichromacy, & tetrachromacy.
2. What type of cone cells account for a human’s “normal color vision”?
3. Why is color vision highly dependent on adaptation and evolutionary factors? In other words, why might nocturnal species, such as bats and owl monkeys, lack color vision?
