How do dogs see the world?

Dog vision is very different from human vision. Dogs see the world in fewer hues than we do, but that doesn’t mean our canine companions are completely color blind. But even though dogs’ visual world isn’t as clear or as colorful as ours, their ability to see movement is superior.



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dog eyes

What colors can dogs see?

The human eye works with three types of color-sensing cells called cones. By comparing how each of these cones is stimulated by incoming visible light, our brain distinguishes red wavelengths from green wavelengths and blue wavelengths from yellow wavelengths. Dog eyes, like those of most other mammals, contain only two types of cones. These allow their brains to distinguish blue from yellow, but not red from green.

Dogs are not completely color blind, but their eyes are structured similarly to those of people with red-green color blindness, whose eyes also lack the third type of cone normally found in humans, Jay Neitz, scientist in color vision at university. from Washington who has conducted many modern experiments on color perception in dogs, told Live Science.

We can get a sense of what dogs see, Neitz said, if we assume their brains interpret signals from their cone cells much like the brains of people with color blindness do.

Related: Red-Green and Blue-Yellow: The Great Colors You Can’t See

To see blue and yellow, dogs and humans rely on neurons inside a part of the eye called the retina. These neurons are fired in response to yellow light detected in cone cells (which are also inside the retina), but neuron activity is suppressed when blue light hits the cones. A dog’s brain interprets the excitation or suppression of these neurons as a sensation of yellow or blue, respectively. However, in dogs and people with color blindness, both red light and green light have a neutral effect on neurons. Without a signal to interpret these colors, the dog’s brain does not perceive any color. Where you see red or green, they see shades of gray.

“A human would miss the sensations of red and green,” Neitz said. “But whether or not the dog’s sensations lack red and green, or whether their brain assigns colors differently, is unclear.”

Also, like people with color blindness, dogs can use other cues to distinguish the color we call “red” from the color we call “green.”

Related: See 15 crazy animal eyes

“Most of the time there are good clues to help them figure it out; for example, red objects tend to be darker than green objects,” Neitz said. “So if it’s a dark apple, a red-green color-blind person will know it’s probably a red apple, and if it’s a lighter apple, it may be a Granny Smith.”

There is evidence that dogs may be able to see colors that humans cannot. A 2014 study published in the journal Proceedings of the Royal Society B found that the lenses of a dog’s eyes transmit significant amounts of ultraviolet light, whereas those wavelengths are blocked by human lenses. This suggests that dogs might see more blue light than we do.

How sharp is the dog’s vision?

In addition to lacking some of the hues perceived by human eyes, dog vision lacks some of the sharpness of human vision. In a 2017 study, published in the journal PLOS One and conducted at Linköping University in Sweden, researchers designed a canine visual acuity test similar to tests ophthalmologists give to humans. Instead of having to discern letters of decreasing size, dogs were rewarded with treats for correctly identifying images containing vertical or horizontal lines with ever-smaller spaces between them.

The researchers found that the dogs – or at least the whippets, pugs and the only Shetland Sheepdog that took part in the experiments – were very nearsighted. The results of the experiment suggest that dogs, in well-lit conditions, have about 20/50 vision. This means that they must be 20 feet (6 meters) from something to see it as well as a human who is 50 feet (15 m) from that same object.

Do dogs have night vision?

While dogs’ night vision is quite blurry, at around 20/250, according to the 2017 study, it’s also much more sensitive than humans’ night vision. Dogs are crepuscular, which means they tend to be most active around dawn and dusk, according to the American Kennel Club. While human eyes are filled with cones, which help detect color and work better in daylight, dog eyes contain more light-sensing cells called rods, which distinguish between dark and light. and are therefore at their best in low light. – light conditions, according to the Merck Veterinary Manual.

Related: See the world through the eyes of a cat

Many dog ​​breeds (but not some of the toy dog ​​breeds) also have a special eye coat, known as the tapetum lucidum, which reflects light back to their retinas, essentially magnifying the light that reaches the rods there, according to a 2014 study in the Journal of Veterinary Medical Science. The tapetum lucidum is what causes dogs’ eyes to glow bluish-green when light shines on them at night, according to the Merck Veterinary Manual.

Take-out? Dogs have better night vision than humans.

Canine motion detection

While you might think dogs live in a dull and fuzzy visual world compared to ours, there’s one area where their vision beats ours: they’re much better at detecting movement. This is due to something called critical flicker fusion rate. Imagine a light that flickers faster and faster. When the light is flashing 60 times per second, humans will believe that the light is shining steadily. According to a 1989 study published in the journal Physiology and Behavior, that same light must flash about 75 times per second to fool a dog.

This ability likely allows dogs to spot moving objects, such as prey, much faster and more accurately than humans.

Bibliography

Byosière, SE, Chouinard, PA, Howell, TJ and Bennett, PC (2017). What do dogs (Canis familiaris) see? A review of vision in dogs and implications for cognitive research. Psychonomic Bulletin and Review25(5), 1798–1813.

Coile, DC, Pollitz, CH and Smith, JC (1989). Behavioral determination of critical flicker fusion in the dog » Physiology and behavior45(6) 1087–1092.

Douglas, RH & G. Jeffery. (2014). The spectral transmission of ocular media suggests that ultraviolet sensitivity is widespread in mammals. Proceedings of the Royal Society B: Biological Sciences, 281(1780).

Hirskyj-Douglas, I. (2016, September 8). This is what dogs see when they watch television. The conversation.

Miller, PE and CJ Murphy. Vision in the dog. (1995). Journal of the American Veterinary Medical Association, 207(12), 1623-1634.