Canine Color Vision

This topic came up on an agility forum, so I dug up my notes on Canine Color Vision, since as a visual artist, this topic interests me greatly!  For those of you interested in this topic, there is a lot to read here. For those of you not that interested, in general Canine color vision is similar to human Red/Green color blindness which translates into dogs seeing blue and yellow very well.  Red and green look rather brown-ish.  I make mental notes about the color of tunnels when walking courses as I believe yellow and blue tunnels are more likely to “suck in” a dog  🙂 than a red or green tunnel, especially if the tunnel is part of a contact/ tunnel discrimination.

http://www.colblindor.com/coblis-color-blindness-simulator/ upload images to this page to see what it would look like to color blind people or dogs

http://www.colour-blindness.com/colour-blindness-tests/ishihara-colour-test-plates/ Link to Ishihara Colour test (ut colored lenses on Yellow Purple and compare R and G

Color vision in the dog.
Dogs can see colors
Dogs not only see in shades of gray but also can see distinct colors contrary to what most people belief. About one hundred years ago some scientific tests were made to find out more about the color vision of dogs. But these tests weren’t that scientific as they thought and the researchers concluded only that color vision doesn’t play a part in the daily life of a dog.
Only about 90 years later distinct researches have shown that dogs can perceive colors. Neitz, Geist and Jacobs researched in 1989 the color vision of domestic dogs and found the following facts:
1.    Dogs have two different color receptors in their eyes and therefore are dichromats.
2.    One color receptor peaks at the blue-violet range, the other at the yellow-green range.
3.    Conclusion: Dogs are green-blind which is one form of red-green color blindness also called deuteranopia.
This results were support by later researches of Jacobs with colleagues in 1993 and Miller and Murphy in 1995.
Abstract
The color vision of three domestic dogs was examined in a series of behavioral discrimination experiments. Measurements of increment-threshold spectral sensitivity functions and direct tests of color matching indicate that the dog retina contains two classes of cone photopigment. These two pigments are computed to have spectral peaks of about 429 nm and 555 nm. The results of the color vision tests are all consistent with the conclusion that dogs have dichromatic color vision.

http://evolutionaryanthropology.duke.edu/dogs Duke U. Canine Cognition Center, Brian Hare, PhD
Dr. Brian Hare, an Assistant Professor of Evolutionary Anthropology at Duke University’s Institute for Brain Sciences.  Hare clinically observes dogs to understand how evolution changes cognition. He is attempting to document canine psychology — ‘dog thinking’ — that currently does not exist in the field of brain science.

http://psychlops.psy.uconn.edu/eric/class/dogvision.html
Includes a statement about: Visual acuity
Visual acuity is the ability to see the details of an object separately and clearly. Visual acuity depends on three factors: a) optical properties of the eye, b)retinal detection and processing of the image, and c) proper interpretation of the images by higher centers in the brain. Postretinal processing has not been extensively studied in dogs, and was beyond the scope of the article being reviewed.
Retinal factors in visual acuity:
It is felt that the retina is the principle limiting factor of visual acuity in dogs. To improve vision in dim light, a greater number of photoreceptors converge on a single ganglion cell (a nerve cell that gathers input from receptor cells and then transmits the information to higher nervous centers in the brain). The more photoreceptors converging on a single ganglion cell, the less detail is present in the image produced, just as high speed photographic film, designed for low light situations, produces a grainier image than lower speed (brighter light) photographic film. The more ganglion cells present, the more nerve fibers present in the optic nerve that relays visual information to the brain. The canine optic nerve contains approximately 167,000 nerve fibers, compared with the human optic nerve which contains 1.2 million nerve fibers.
Estimates of visual acuity:
The most commonly used indicator of visual acuity is the Snellen fraction, which relates the ability to distinguish objects or letters at a fixed distance with the standard response. Snellen fractions of 20/20, 20/40, 20/60 or 20/100 indicates that the test subject needs to be 20 feet away from an image to clearly visualize the details that a normal subject could discern at 20, 40, 60, and 100 feet away, respectively. A variety of studies have been done, using a number of different methodologies, to estimate the visual acuity of dogs. We can assume from these studies that the normal dog has a visual acuity of approximately 20/75. This means that a dog must be 20 feet away from an object to clearly visualize details of that object that a human with normal vision could clearly visualize from a distance of 75 feet. Again, this less acute vision in dogs is a trade-off for improved vision in dim light, and their life style does not require visual distinction of fine details as does our life style.
Color vision

A number of studies have been done to investigate the color vision of dogs, and the results have been conflicting. However, more recent, better controlled studies indicate that dogs do possess and use color vision, but not to the same degree that humans do. The photoreceptor used for color vision is the cone, and there are cones present in the canine retina. However, they are present in low numbers, comprising less than 10% of the total photoreceptor population in the central area of the retina, as opposed to the human retina which consists of nearly 100% cones in the fovea. Two distinct type of cones appear to be present in the canine retina. One type is maximally sensitive to light in the wavelength that appears violet to people, and the other type is maximally sensitive to light in the wavelength that appears yellow-green to people. Thus, it appears that the visual spectrum of color in dogs is divided into two hues; one in the violet and blue-violet range, probably appearing as blue, and the other in the greenish-yellow, yellow, and red range, which is probably seen as yellow. Light that appears blue-green to people probably appears as white or shades of gray to dogs. Dogs are unable to differentiate colors that appear as green, yellow-green, orange or red to people, and are unable to differentiate greenish-blue from gray. This is similar to people who are red-green color blind. However, one study indicates that dogs are better able to differentiate between subtle shades of gray than people, which would be advantageous in increasing visual discrimination in low light conditions, where insufficient light is available to stimulate cones.
Summary

The authors conclude by stating that although the canine visual system may be considered inferior to the human visual system in such aspects as degree of binocular overlap, color perception, accommodative range, and visual acuity, the canine visual system is superior to the human visual system in other aspects, such as functional ability in low light conditions, retinal response rate to another image (flicker fusion), field of view, ability to differentiate shades of gray, and possibly the ability to detect motion. The canine visual system is optimized to exploit a different environmental niche than our own, and hopefully by better understanding the strengths and weaknesses of the canine visual system we will be better able to understand our hunting companion’s capabilities. Let me conclude by encouraging those of you interested in this issue to read the complete article, which includes 68 references to other works. I wish to personally thank the authors for greatly improving my own understanding of the canine visual system.
http://agilitynet.co.uk/health/caninevision_markplonsky.html
By Sarah Probst
Information Specialist
University of Illinois, College of Veterinary Medicine

Owners who want to better understand their canine companions must recognise that dogs see the world from a different visual perspective. The differences begin with the structure of the eye. ‘We have a good idea what canines see because we know the make-up of the retina of a dog’s eye,’ says Dr. Ralph Hamor, a veterinarian and specialist in ophthalmology at the University of Illinois College of Veterinary Medicine Teaching Hospital.
The retina, which covers the back of the inside of the eyeball, contains cones and rods-two types of light-sensitive cells. Cones provide color perception and detailed sight, while rods detect motion and vision in dim light. Dogs, which have rod-dominated retinas, see better in the dark than humans do and have motion-oriented vision. However, because they have only about one-tenth the concentration of cones that humans have, dogs do not see colors as humans do.
‘I generally explain that dogs see like a color-blind human,’ says Dr. Hamor. ‘Many people think that a person who is red/green color blind cannot see any color, but there are variations of being color blind. Most people have vision that is trichromatic (three color variations). People who are red/green color blind are dichromatic (two color variations).
Dogs can pick out two colors-blue-violet and yellow-and they can differentiate among shades of gray.’ Dogs are unable to distinguish among green, yellow, orange, and red. They also have difficulty differentiating greens and grays.
Dogs use other cues (such as smell, texture, brightness, and position) rather than rely on color. Seeing-eye dogs, for example, may not distinguish whether a stoplight is green or red; they look at the brightness and position of the light. This and the flow and noise of traffic will tell the dog that it is the right time to cross the street.
The set of dog’s eyes determines the amount of field of view and depth perception. Prey species tend to have eyes set on the sides of their head because the increased field of view allows them to see approaching predators. Predator species, like humans and dogs, have eyes set closer together. ‘Human eyes are set straight forward while dog eyes, depending on the breed, are usually set at a 20 degree angle. This angle increases the field of view and therefore the peripheral vision of the dog.’
However, this increased peripheral vision compromises the amount of binocular vision. Where the field of view of each eye overlaps, we have binocular vision, which gives us depth perception. The wider-set eyes of dogs have less overlap and less binocular vision.
Dogs’ depth perception is best when they look straight ahead, but is blocked by their noses at certain angles. ‘Predators need binocular vision as a survival tool,’ Dr. Hamor says. Binocular vision aids in jumping, leaping, catching, and many other activities fundamental to predators.
In addition to having less binocular vision than humans, dogs also have less visual acuity. Humans with perfect eyesight are said to have 20/20 vision-we can distinguish letters or objects at a distance of 20 feet. Dogs typically have 20/75 vision-they must be 20 feet from an object to see it as well as a human standing 75 feet away. Certain breeds have better acuity. Labradors, commonly used as seeing-eye dogs, have been bred for better eyesight and may have closer to 20/20 vision.
Don’t expect your dog to recognize you across the field by sight. He’ll recognize you when you do some sort of motion particular to yourself or by smell or hearing. Because of the number of rods in the retina, dogs see moving objects much better than they do stationary objects. Motion sensitivity has been noted as the critical aspect of canine vision. ‘So much of dog behaviour deals with posture and appropriateness. Small changes in your body posture mean a lot to your dog,’ Dr. Hamor adds. Dog owners need to modify training based on this fact. If you want your dog to perform an action based on a silent cue from you, Dr. Hamor suggests using a wide sweeping motion to cue your dog.
When dogs go blind, owners often wonder if the dogs’ quality of life has diminished to the point where they are no longer happy. ‘We know that humans deal well with being blind, and humans are much more dependent on their eyes than are dogs,’ Dr. Hamor says. ‘Blind dogs lead happy lives if they are comfortable.’ The owner may need to make some adjustments in the pet’s environment, such as having a fenced yard, taking leashed walks, and not leaving unusual objects in normal pathways. ‘When blind dogs are in their normal environment, most people don’t know they are blind.’ When clients visit Dr. Hamor asking about quality of life for their newly blind dog, Dr. Hamor suggests that they take a month to see if they and their dog are happy. In the majority of cases, the owners never come back.

http://www.uwsp.edu/PSYCH/dog/LA/DrP4.htm
Canine Vision
by Mark Plonsky, Ph.D.
Summary
Dogs are red-green color blind. They see a brighter and less detailed world when compared to humans. Peripheral vision is better than humans (dogs see more of the world), but distance is not judged quite as well. Dogs excel at night vision and the detection of moving objects. Figure 1 is a rough guesstimate of what a dog and human might see when viewing a color band (the electromagnetic spectrum).

These differences in visual ability make sense in light of evolutionary theory. Good depth perception and visual acuity are necessary for a primate (from which humans evolved) jumping from tree limb to tree limb. Good color vision enabled this primate to choose the ripest and most nutritious fruit. The canine, on the other hand, is well adapted as a nocturnal hunter of camouflaged prey.
Particulars
1.    Color
Dogs see something like a human deuteranope, that is, they are red-green color blind (occurs in 4% of male humans). Simply put, this is due to having only 2 cone types rather than 3 (light sensitive cells include cones and rods).
2.    Detail or Acuity
Since dogs have no fovea (or area with 100% cones), their estimated eye for detail is (roughly) 6 times poorer than in an average human.
3.    Night Vision
Dogs have much better night vision for 2 reasons:
o    The have more rods (which enable night vision).
o    They have a structure called the Tapetum Lucidum
This is a reflective surface behind the retina (area including the light sensitive cells) that reflects light back through it (gives the eerie shine at night).
4.    Sensitivity to Movement
Dogs are better able to detect movement.
5.    Depth & Field
Figure 2 show the field of view of a human and a dog. Due to the placement of the eyes, humans have an overlap of the field of each eye of 140; in dogs, it is about 100.

This results in the dog having limited ability to accommodate (focus on items at different distances), but a wider overall field allowing them to see more of the world.

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