Are Dogs Color Blind? How Do We Know What Colors Dogs Can See? · Kinship

Dog eyesight 101

Eyesight results from some incredibly complex interactions between light, lenses, nerves, and some jelly. At a basic level, light is electromagnetic radiation, and color is perceived based on the wavelengths of this radiation. Humans, animals, insects, and birds all detect and distinguish between different ranges of this radiation. The visible spectrum, which is perceived as light and color, is a relatively small part of the overall electromagnetic spectrum, which includes very high frequency waves like X-rays and very low frequency radiation like radio.

When electromagnetic energy in the visible spectrum reaches the eye, it encounters the clear surface of the eye, called the cornea. The cornea’s curved surface helps direct light from a wide area into the eye’s anterior chamber. The anterior chamber helps the surface of the eye maintain its rounded shape and allows light to pass through the pupil without interference.

The pupil is an opening that can open wide in low-light conditions to allow more light in. It can also constrict in bright conditions to prevent overloading the eye with light and washing out the image. The lens sits immediately behind the pupil and focuses light into the back of the eye. The lens of the eye is normally clear, but defects like cataracts can affect its ability to allow light through and to focus it properly.

The vitreous humor is a clear, jelly-like substance that fills the back part of the eye. It helps maintain the eye’s shape, allows light through to the retina, and provides nutrition to cells on the surface of the retina. The retina is where the really complex stuff happens. The surface of the retina consists of rods and cones, which are specialized nerve cells that are stimulated by light.

Rods are very sensitive to light and greatly outnumber cones, which provide color vision. Because rods are so plentiful and so sensitive, they’re very helpful in low-light situations. They may not provide the same level of detail as cones, but they still provide the vital function of allowing vision in low-light conditions.

The reflective tapetum gives dogs a bonus to their low-light vision by reflecting light that was not initially captured by the retina back onto the nerves. This reflective layer of the retina gives dog eyes their yellow-greenish glow. The improvement in low-light vision comes at a cost though — the scattering of light during reflection decreases the sharpness of what a dog sees.

Cones contain different photopigments sensitive to specific wavelengths of light. In most humans, there are usually three types:

• Short wavelength cones are more sensitive to light in the blue wavelength range.

• Medium wavelength cones are more likely to pick up light in the green range.

• Long wavelength cones have sensitivity to light in the red spectrum.

The relative number of rods and cones stimulated gives the brain information about brightness, contrast, and color. The visual center of the brain converts this into the usable information that we think of as vision.

How do we know dogs are color blind?

The idea of dogs only seeing in black in white is likely due to a misconception. Dog color blindness is similar to human red-green color blindness (dichromatism). Early attempts at testing dogs’ reactions to different colors provided mixed results, but testing over the past forty years provided a consistent answer about what colors dogs can see.

The study of color vision in dogs relies both on laboratory examination of the cells in their eyes and real-world testing of their capabilities. The proportion of rods in the center of a dog’s retina is much higher than it is in people. This means that they likely prioritize low-light vision over color perception. Examination of the photopigments in dogs’ cones cells showed that they were of a slightly different type than those in people. Dogs’ cones pick up color in the violet-to-blue range and in the greenish–yellow-to-red range; this leaves minimal information about colors in the bluish-green range, which dogs likely see as gray.

Real-world testing of dogs’ vision lines up with these microscopic observations. Tests involving retinal stimulation and dogs’ ability to discriminate between two different-colored objects show that dogs can perceive and act on differences in color.

What colors can dogs see?

Based on testing, we are reasonably confident that dogs’ eyes can pick up colors similar to a person with red-green color blindness. This means that dogs most likely see things in shades of gray, blue, and yellow. Dogs likely perceive some shades of green as gray, while orange and some reds may appear yellowish. Deep, dark reds may seem to be a muddy brownish color.

Are all dogs color blind and limited to seeing only these two colors? It’s hard to know for sure. For example, people with tetrachromacy have four types of cones. This genetic mutation is rare and very difficult to detect in humans. It’s possible that some dogs may have a genetic change that results in the production of an extra type of cone, but they likely wouldn’t be identified unless they were one of the extremely small number of dogs that happen to take part in vision studies.

The other big question is if dogs process and perceive color information in the same way humans do? Color perception may be slightly different for each person — we can agree that the sky is blue, but do we see the exact same shade of blue? After all, what color was that dress? Dogs may perceive color differently than people do, but color does seem to be an important part of their decision-making process.

A 2013 study evaluated whether dogs would pursue a reward based more on the color or brightness of stimuli. Dogs consistently chose based on color, showing that they likely consider color information more strongly than brightness alone.

A 2017 study used a modified version of the Ishihara test for color blindness in people. This is a test that you’re likely familiar with, featuring a pattern of dots that form differently colored numbers or shapes. The test was modified in dogs so that the colored dots formed the shape of a running cat, which animated and played in a loop. In the study, the dogs’ reaction to the animation was used to determine which color of moving dots they were able to pick out against a gray background.

Despite the difficulty in figuring out how to know what a dog is seeing and if their reaction to visual testing is not influenced by other factors, researchers have done a good job of showing that dogs can distinguish some colors. While their color vision is not as deep as most people’s, dogs still rely on it in their day-to-day life.

References

• “Eyes and Spectrometers.” Upenn.edu, 2022, www.sas.upenn.edu/~ksundeen/spec%20project%20stuff/Eyes%20and%20Spectrometers.html.

• Jordan, Gabriele, and John Mollon. “Tetrachromacy: The Mysterious Case of Extra-Ordinary Color Vision.” Current Opinion in Behavioral Sciences, vol. 30, Dec. 2019, pp. 130–134, vision.psychol.cam.ac.uk/jdmollon/papers/JordanMollon2019Tetrachromacy.pdf, https://doi.org/10.1016/j.cobeha.2019.08.002. Accessed 5 May 2020.

• Kasparson, Anna A., et al. “Colour Cues Proved to Be More Informative for Dogs than Brightness.” Proceedings. Biological Sciences, vol. 280, no. 1766, 7 Sept. 2013, p. 20131356, www.ncbi.nlm.nih.gov/pubmed/23864600, https://doi.org/10.1098/rspb.2013.1356.

• Neitz, Jay, et al. “Color Vision in the Dog.” Visual Neuroscience, vol. 3, no. 2, Aug. 1989, pp. 119–125, https://doi.org/10.1017/s0952523800004430.

• Pongrácz, Péter, et al. “Do You See What I See? The Difference between Dog and Human Visual Perception May Affect the Outcome of Experiments.” Behavioural Processes, vol. 140, July 2017, pp. 53–60, https://doi.org/10.1016/j.beproc.2017.04.002. Accessed 21 Aug. 2020.

• Purves, Dale, et al. “Cones and Color Vision.” National Library of Medicine, Sinauer Associates, 2012, www.ncbi.nlm.nih.gov/books/NBK11059/.‌

• Siniscalchi, Marcello, et al. “Are Dogs Red–Green Colour Blind?” Royal Society Open Science, vol. 4, no. 11, Nov. 2017, p. 170869, https://doi.org/10.1098/rsos.170869.