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The belief that dogs are colorblind, in the sense that they see the world only in black and white and shades of gray, is a common misconception. In a series of painstaking and extended measurements Jay Neitz at the University of California, Santa Barbara, established that dogs do have color vision (see here). However the range of colors that dogs see is much more limited than the range of colors that we humans see. This is because human beings have three different types of color receptors (the cones in the retina) each of which is tuned to a different range of wavelengths, while dogs have only two types of color receptors (and many fewer of these proportionally). This means that dogs can still see colors, but their visual world is reduced to yellows, blues, and shades of gray. Furthermore the reduced number of cones in the canine retina may indicate that the colors that dogs see are not as intense. In the figure below you can compare what a human being might see to what a dog might see.
Most researchers understand that color vision in dogs is useful because it helps to allow them to see things which might be difficult or blurry because their extreme farsightedness puts near objects out of focus. However because of dogs' limited range of color vision, the majority of scientists have long believed that they seldom choose to use color information to discriminate between objects. The guess is that dogs rely upon the brightness or darkness of the objects rather than color when making decisions.
You might think that if an animal has a particular sensory ability, they would certainly use it when making conscious choices. However this is far from always the case. For example, compared to dogs humans have a limited ability to discriminate scents. However we still use information gathered by our nose even if it is not at the conscious level. Thus scientists have shown that there is a pheromone (that is a biological scent) that is given off by babies and young children. Humans, especially women, respond to that odor in a protective and affectionate way. For example if women are shown a series of photographs of children, some of which have been smeared with this pheromone, they will judge the photographs with the scent as being more attractive, even though they are not consciously aware of the scent. Similarly there are sex related pheromones which make adults more attractive to one another even though we are not consciously aware of them, and, as you might guess, perfume manufacturers take advantage of this by using them as additives.
Because the question of how much dogs use color vision was unresolved, Anna Kasparson, Jason Badridze and Vadim Maximov, researchers from the Russian Academy of Sciences in Moscow, and Ilia State University in Tbilisi, decided to see if dogs consciously choose to use the color vision information that is available to them, and whether they would prefer to use color over brightness information. This work is described in a recent paper in the Proceedings of the Royal Society B.
The experiment itself was rather simple in concept, although it took extended testing. They started out by printing four pieces of paper colored dark yellow, light yellow, dark blue, and light blue. They chose these colors because they contained two different visual dimensions which dogs ought to be able to discriminate, namely the color (yellow or blue) and the brightness (dark or light). In the training phase of the experiment the dogs were presented with two boxes, each containing a bit of meat, but only one of these was unlocked. A colored card, either dark yellow or light blue was propped up in front of each box. For each dog one of these cards was designated as correct and was associated with an unlocked box from which he could get the treat. Each dog received 10 training trials every day for nine days. The dogs learned this discrimination quickly and at the end of the training period all of the dogs were performing virtually perfectly. Testing took place over the next 10 days. In the middle of the usual practice sessions on one trial the cards were changed so that now one was a dark blue and the other a light yellow. Suppose that the dog had been trained so that the dark yellow was correct. The researchers reasoned that on this test trial when presented with a light yellow and a dark blue, if the dog was making his choices based upon brightness alone he would select the dark blue, however if the dog was actually using the color information consciously then he would still choose the yellow even though it was now the brighter one of the pair.
The results were unambiguous. All of the dogs went for the color-based choice more than 70% of the time and six out of the eight dogs chose it 90 or 100% of the time. Contrary to what many scientists might have predicted, the dogs were clearly basing their choice on the color associated with getting the meat reward rather than whether the card was dark or light. This means that dogs were using color information as the basis of their conscious choices.
This is a small but useful increment in our knowledge of how dogs see and process their world. It tells us that we can use different colors as training aids and cues for our dogs. But we have to choose our colors correctly. Choosing a red versus a green color will only confuse our dogs because that pairing does not fit in with the color discriminations that dogs can easily make. Still it is nice to know that the dog's-eye view the world is more colorful than many of us had believed before.
For more about color vision in dogs and how it compares to color vision in humans click here.
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