what do we look like to nocturnal eyes?
11-27-2006, 10:18 AM
#1
Nontypical Buck
Thread Starter
Join Date: Sep 2006
Location: YewNork
Posts: 1,794
what do we look like to nocturnal eyes?
i always wonder how in the pitch black of dark a deercan spot me in a tree, does anyone have any pictures of how we look to a deer at night or explain it?
11-27-2006, 10:27 AM
#2
Boone & Crockett
Join Date: Oct 1998
Location: Hughesville, PA USA
Posts: 18,322
RE: what do we look like to nocturnal eyes?
I understand that's when the black and white comes into play. In daylight deer supposedly see in dichromacy. Here: http://www.enigmacamo.com/test_photos.htm
11-27-2006, 02:18 PM
#7
Giant Nontypical
Join Date: Feb 2003
Location:
Posts: 7,571
RE: what do we look like to nocturnal eyes?
I don't believe that deer are considered totally nocturnal. Anyway, here is some good info.
[align=center]SCOTOPIC VISION[/align]
Many subtle differences in physiology make the deer far more sensitive to dim light, especially shorter wavelengths. They switch to black and white rod vision as humans do but can detect light 1000X below our threshold in the blue and U-V wavelengths. The black and white (Rod) vision in Low Light where the cones can not function is called Scotopic Vision. (See inside cover)
[align=center]
[/align]Atsko Inc.
2530 Russell S. E.
Orangeburg, SC 29115
Dear Mr. Gutting
In response to your inquiry about the visual capabilities of game animals, I have attempted to compile the current scientific knowledge with a minimum of specialized jargon.
VISUAL SENSITIVITY
Grazing animals depend on keen vision at dawn, dusk and night in order to survive. Their eyes are specialized to see best under very low light conditions in which we can barely see or cannot see at all.
The extraordinary capability of grazing animals to see in dim light (and even almost no light) is because:
1) Their pupil can open wider to admit more light. Since it is the total area of the pupil that is important, the light gathering power of the eye increases as the square of the pupil diameter. Thus, an eye of about the same size as the human eye with a pupil that can open to three times the diameter of the human pupil gathers 32 or 9 times more light. (Note that it is not the eye size that is important for visual sensitivity but rather the size of the pupil relative to eye size. Large eye size is important, however, for good resolution of detail).
2) Vision is initiated when light entering the pupil strikes the retina—the light sensitive layer of tissue at the back of the eye that is analogous to the film in a camera. The retina contains two kinds of light-sensitive receptor cells, rods and cones. The cones are responsible for day-time vision and color vision. Rods are responsible for vision in dim light. The central region of the human eye (the fovea) on which we depend on most for vision is tightly packed with cones but contains no rods. The rest of the human retina contains both rods and cones. The ratio of rods to cones increases in the periphery of the human retina.
3) Ungulates (hoofed animals) also have both rods and cones but rods predominate (even in the central area) making up well over 90 percent of the total photoreceptors over the entire area of the retina. The rods are incredibly sensitive to light—about one-thousand times more sensitive than cones. The high ratio of rods to cones in the eyes of ungulates makes them very sensitive to dim light and especially sensitive to shorter wavelengths of light as described below.
Ungulates, cats, dogs, and predators have a reflective layer in back of the retina that greatly enhances sensitivity. This reflector is called a reflective tapetum. We see the effect of the reflective tapetum as “eye shine” in animals. Human eyes don’t shine at night because light that transits the retina without being absorbed by a photoreceptor cell is lost, absorbed by a black layer (the pigment epithelium) at the back of the eye. The effect of the tapetum for the animal is that light that passes through the retina without activating a photoreceptor the first time is “recycled”—reflected back to the photoreceptors for a second chance.
4) The human lens contains a filter that blocks UV light from reaching the retina. The UV filter in the human lens has a yellow appearance and also absorbs heavily in the violet and blue. This filter is not present in the lens of ungulates. They receive much of the UV light that we filter out.
In daylight, vision is based on cones that are most sensitive to middle and long wavelength lights. The yellow filter in our lens probably serves two purposes. First short wavelength light (blue, violet, and UV) is scattered and refracted much more in the eye than long wavelength light (yellow, orange, and red). If it were not filtered out by the lens the short wave light would fuzz the retinal image slightly and interfere with our ability to see fine detail. Expert marksmen know that acuity can even be further improved by wearing glasses with yellow lenses that block more blue light than the human lens. The other purpose of the UV blocking filter in the human lens is that it appears to protect the retina from UV damage. This damage probably progresses very slowly over decades of life, so protection is less important for animals with much shorter life spans than humans. As daylight fades to night, light levels drop below the threshold for cones and vision depends on rods. Unlike cones that are sensitive primarily to longer wavelengths the rods are most sensitive to shorter wavelengths. This transition from long wave sensitivity to short wave sensitivity that occurs during dark adaptation is termed the Purkinje shift. The rod sensitivity is highest to wavelengths near 500 nm (the blue green region of the spectrum). Rod sensitivity drops off quickly for wavelengths longer than 500 nm, but stays fairly high for wavelengths shorter than 500 nm, even into the ultraviolet.
The price that humans pay for protection from the UV Iight and slightly higher acuity in day light that is provided by the UV blocking filter is an extreme loss of sensitivity to much of the spectrum where rods are sensitive. 400 nm is the wavelength that is usually considered to be the break point between visible and ultraviolet light. This is because the average human lens absorbs 94% of the light at 400 nm and its absorption increases dramatically for wavelengths shorter than that. We do not see UV because it never reaches the retina. Animals without the UV filter have an enormous advantage over humans in ultraviolet sensitivity. For example, rod sensitivity is still fairly high to UV Iight with a wavelength of 380 nm (long wave UV). The lens in the human eye blocks over 99% of this light. This means that based on this factor alone eyes that don’t block UV will be over 100 times more sensitive to 380 nm light than humans.
One can easily see that with all these factors multiplied together, under many conditions, ungulates are expected to see hundreds of times better in dim light than humans. Under some special circumstances their advantage is even much greater. A distant object reflecting UV Iight whose image fell on the central region of the retina would be an incredible million times more visible to a carnivore or ungulate than it is to a human.
Humans are much better visually equipped than any game animal to read the fine print on a topo map at noon on a sunny day. But game animals are thousands of times better equipped to see objects that reflect short wavelength light under dim conditions.
Birds—Many birds are also sensitive to UV Iight. Their lenses also lack a UV filter. But, their sensitivity to UV comes about for a much different reason than in ungulates. Most birds are active in day-light and their retinas have a high concentration of cone photoreceptors. However, they have a type of cone photoreceptor that is not present in humans—a cone that is specifically sensitive to UV Iight. Scientists believe that many birds may actually see UV Iight as a separate color that is different than any of the three primary colors seen by humans.
COLOR VISION
The ability to see color is an important aspect of human vision. Color differences often allow us to easily identify objects from their backgrounds that would otherwise be invisible. For example, at a distance, ripe red tomatoes on the vine are much more easily seen among the leaves than unripe green ones.
Humans are able to see color because of three different types of cone photoreceptor cells in the retinas of their eyes. One cone type is most sensitive to short wavelength (blue) lights a second is most sensitive to middle wavelengths (green) and a third is most sensitive to long wavelength (red) lights. The three different cone types are the basis for what has been termed trichromatic (literally three-color) vision in humans. It should be noted as an aside that the majority of the cone photoreceptors in the human retina are the long-wavelength sensitive type, the middle wavelength sensitive type are the next most common, and the short wavelength sensitive are rare—only about 10% of the cones. The blue sensitive cones are important for color vision, but because of their small number they provide little or no over-all sensitivity to short wavelength light.
Scientists have studied color vision capacities in a number of animals. Among mammals, only primates (monkeys and apes) have been found to have trichromatic color vision like that of humans. However, a number of other mammals have color vision that is based on only two different cone types; this is dichromatic (two-color) vision. This simplified type of color vision seems to be common among mammals and has been observed in carnivores (e.g. dogs and cats) and ungulates (hoofed mammals). Although vision is predominantly based on rods in these animals (more than 90 percent of the total photoreceptors in their eyes are rods giving them excellent night vision), they have enough cones to provide color vision. Obviously color vision based on only two different cone types is not going to be as good as human color vision that is based on three types. The deficiency in dichromatic color vision is in the ability to discriminate among the colors of objects that reflect light in the middle to long wavelengths, i.e. green, yellow, brown, orange, and red. The ungulates and carnivores with color vision based on only short wavelength sensitive cones and long wavelength sensitive cones, would find these colors difficult or impossible to distinguish. However, for these animals, blue, violet and near ultraviolet (which is invisible to us because it is blocked by the lens) stand out from the other colors. The colors of earthly objects are mostly browns, tans, greens and yellows. To an animal with dichromatic color vision, a sportsman wearing garments that strongly reflect short wavelength light would stand out against these backgrounds like a ripe red tomato on a green vine.
Sincerely Yours,
Jay Neitz, Ph.D.
Vision Scientist
[align=center]SCOTOPIC VISION[/align]
Many subtle differences in physiology make the deer far more sensitive to dim light, especially shorter wavelengths. They switch to black and white rod vision as humans do but can detect light 1000X below our threshold in the blue and U-V wavelengths. The black and white (Rod) vision in Low Light where the cones can not function is called Scotopic Vision. (See inside cover)
[align=center]
[/align]Atsko Inc.2530 Russell S. E.
Orangeburg, SC 29115
Dear Mr. Gutting
In response to your inquiry about the visual capabilities of game animals, I have attempted to compile the current scientific knowledge with a minimum of specialized jargon.
VISUAL SENSITIVITY
Grazing animals depend on keen vision at dawn, dusk and night in order to survive. Their eyes are specialized to see best under very low light conditions in which we can barely see or cannot see at all.
The extraordinary capability of grazing animals to see in dim light (and even almost no light) is because:
1) Their pupil can open wider to admit more light. Since it is the total area of the pupil that is important, the light gathering power of the eye increases as the square of the pupil diameter. Thus, an eye of about the same size as the human eye with a pupil that can open to three times the diameter of the human pupil gathers 32 or 9 times more light. (Note that it is not the eye size that is important for visual sensitivity but rather the size of the pupil relative to eye size. Large eye size is important, however, for good resolution of detail).
2) Vision is initiated when light entering the pupil strikes the retina—the light sensitive layer of tissue at the back of the eye that is analogous to the film in a camera. The retina contains two kinds of light-sensitive receptor cells, rods and cones. The cones are responsible for day-time vision and color vision. Rods are responsible for vision in dim light. The central region of the human eye (the fovea) on which we depend on most for vision is tightly packed with cones but contains no rods. The rest of the human retina contains both rods and cones. The ratio of rods to cones increases in the periphery of the human retina.
3) Ungulates (hoofed animals) also have both rods and cones but rods predominate (even in the central area) making up well over 90 percent of the total photoreceptors over the entire area of the retina. The rods are incredibly sensitive to light—about one-thousand times more sensitive than cones. The high ratio of rods to cones in the eyes of ungulates makes them very sensitive to dim light and especially sensitive to shorter wavelengths of light as described below.
Ungulates, cats, dogs, and predators have a reflective layer in back of the retina that greatly enhances sensitivity. This reflector is called a reflective tapetum. We see the effect of the reflective tapetum as “eye shine” in animals. Human eyes don’t shine at night because light that transits the retina without being absorbed by a photoreceptor cell is lost, absorbed by a black layer (the pigment epithelium) at the back of the eye. The effect of the tapetum for the animal is that light that passes through the retina without activating a photoreceptor the first time is “recycled”—reflected back to the photoreceptors for a second chance.
4) The human lens contains a filter that blocks UV light from reaching the retina. The UV filter in the human lens has a yellow appearance and also absorbs heavily in the violet and blue. This filter is not present in the lens of ungulates. They receive much of the UV light that we filter out.
In daylight, vision is based on cones that are most sensitive to middle and long wavelength lights. The yellow filter in our lens probably serves two purposes. First short wavelength light (blue, violet, and UV) is scattered and refracted much more in the eye than long wavelength light (yellow, orange, and red). If it were not filtered out by the lens the short wave light would fuzz the retinal image slightly and interfere with our ability to see fine detail. Expert marksmen know that acuity can even be further improved by wearing glasses with yellow lenses that block more blue light than the human lens. The other purpose of the UV blocking filter in the human lens is that it appears to protect the retina from UV damage. This damage probably progresses very slowly over decades of life, so protection is less important for animals with much shorter life spans than humans. As daylight fades to night, light levels drop below the threshold for cones and vision depends on rods. Unlike cones that are sensitive primarily to longer wavelengths the rods are most sensitive to shorter wavelengths. This transition from long wave sensitivity to short wave sensitivity that occurs during dark adaptation is termed the Purkinje shift. The rod sensitivity is highest to wavelengths near 500 nm (the blue green region of the spectrum). Rod sensitivity drops off quickly for wavelengths longer than 500 nm, but stays fairly high for wavelengths shorter than 500 nm, even into the ultraviolet.
The price that humans pay for protection from the UV Iight and slightly higher acuity in day light that is provided by the UV blocking filter is an extreme loss of sensitivity to much of the spectrum where rods are sensitive. 400 nm is the wavelength that is usually considered to be the break point between visible and ultraviolet light. This is because the average human lens absorbs 94% of the light at 400 nm and its absorption increases dramatically for wavelengths shorter than that. We do not see UV because it never reaches the retina. Animals without the UV filter have an enormous advantage over humans in ultraviolet sensitivity. For example, rod sensitivity is still fairly high to UV Iight with a wavelength of 380 nm (long wave UV). The lens in the human eye blocks over 99% of this light. This means that based on this factor alone eyes that don’t block UV will be over 100 times more sensitive to 380 nm light than humans.
One can easily see that with all these factors multiplied together, under many conditions, ungulates are expected to see hundreds of times better in dim light than humans. Under some special circumstances their advantage is even much greater. A distant object reflecting UV Iight whose image fell on the central region of the retina would be an incredible million times more visible to a carnivore or ungulate than it is to a human.
Humans are much better visually equipped than any game animal to read the fine print on a topo map at noon on a sunny day. But game animals are thousands of times better equipped to see objects that reflect short wavelength light under dim conditions.
Birds—Many birds are also sensitive to UV Iight. Their lenses also lack a UV filter. But, their sensitivity to UV comes about for a much different reason than in ungulates. Most birds are active in day-light and their retinas have a high concentration of cone photoreceptors. However, they have a type of cone photoreceptor that is not present in humans—a cone that is specifically sensitive to UV Iight. Scientists believe that many birds may actually see UV Iight as a separate color that is different than any of the three primary colors seen by humans.
COLOR VISION
The ability to see color is an important aspect of human vision. Color differences often allow us to easily identify objects from their backgrounds that would otherwise be invisible. For example, at a distance, ripe red tomatoes on the vine are much more easily seen among the leaves than unripe green ones.
Humans are able to see color because of three different types of cone photoreceptor cells in the retinas of their eyes. One cone type is most sensitive to short wavelength (blue) lights a second is most sensitive to middle wavelengths (green) and a third is most sensitive to long wavelength (red) lights. The three different cone types are the basis for what has been termed trichromatic (literally three-color) vision in humans. It should be noted as an aside that the majority of the cone photoreceptors in the human retina are the long-wavelength sensitive type, the middle wavelength sensitive type are the next most common, and the short wavelength sensitive are rare—only about 10% of the cones. The blue sensitive cones are important for color vision, but because of their small number they provide little or no over-all sensitivity to short wavelength light.
Scientists have studied color vision capacities in a number of animals. Among mammals, only primates (monkeys and apes) have been found to have trichromatic color vision like that of humans. However, a number of other mammals have color vision that is based on only two different cone types; this is dichromatic (two-color) vision. This simplified type of color vision seems to be common among mammals and has been observed in carnivores (e.g. dogs and cats) and ungulates (hoofed mammals). Although vision is predominantly based on rods in these animals (more than 90 percent of the total photoreceptors in their eyes are rods giving them excellent night vision), they have enough cones to provide color vision. Obviously color vision based on only two different cone types is not going to be as good as human color vision that is based on three types. The deficiency in dichromatic color vision is in the ability to discriminate among the colors of objects that reflect light in the middle to long wavelengths, i.e. green, yellow, brown, orange, and red. The ungulates and carnivores with color vision based on only short wavelength sensitive cones and long wavelength sensitive cones, would find these colors difficult or impossible to distinguish. However, for these animals, blue, violet and near ultraviolet (which is invisible to us because it is blocked by the lens) stand out from the other colors. The colors of earthly objects are mostly browns, tans, greens and yellows. To an animal with dichromatic color vision, a sportsman wearing garments that strongly reflect short wavelength light would stand out against these backgrounds like a ripe red tomato on a green vine.
Sincerely Yours,
Jay Neitz, Ph.D.
Vision Scientist
